On board the TARDIS, all seems well. Vicki tends to an old clock in the console room while the Doctor busies himself at the controls. It is very quiet in the ship, now missing two of its regular occupants. The Doctor misses them very much, even though he knew they had to leave him some day. He also misses his granddaughter and fears that he is pressuring Vicki to stay. But she assures him she's got nothing "at home" to return to and that she is glad to be with him.

Suddenly there is a noise from the living quarters. Some one or some thing has gotten inside the ship. Vicki fears it could be a surviving Dalek and she and the Doctor prepare to face it down. The doors swing open and a figure emerges. It is not a Dalek but a human - Steven Taylor, the young astronaut the Doctor and Vicki encountered on Mechanus. He pitches forward and falls to the floor, still clutching his stuffed panda mascot. Vicki and the Doctor hurry to help him.

Meanwhile, the TARDIS materialises on a rocky seashore against a cliff. From the clifftop above, the arrival is watched by a man in an old-fashioned monk's habit. He is stunned by what he sees, but not for the simply reason of seeing a police box fade into existence where it shouldn't be. The Monk seems very interested in this phenomenon, but does not seem surprised by it at all. He wonders aloud, a strange dark-jewelled ring glittering in the sun as he strokes his chin.

Steven is now conscious and seated in a chair. The Doctor gives him water and he drinks thirstily. Both he and Vicki had thought Steven dead when he went back into the Mechanoid city to rescue his panda mascot, but he is alive and recovering. Steven explains that he got down from the burning city at the last second and then went in search of the Doctor and his friends. He reached the Doctor's ship but remembers little after that. He breathlessly marvels at the interior "the Doc's" ship, his mind moving in all directions. The Doctor lays down two conditions - sit and rest a while, and never call him "Doc" again - and says he is willing to accept the wayward astronaut at his face value.

Vicki returns Steven's panda, Hi-Fi, to him and they both praise his luck for finding the TARDIS. Steven is still confused, though. He can see the large sophisticated interior of the ship, but he remembers only a small blue box in the jungle. Vicki assures him he was not hallucinating and tries to acquaint him with the different dimensions of the ship. She also tells him that that this is a time machine which he does not believe. The Doctor is unhelpful, refusing to confirm or deny anything for this young upstart. Vicki explains the acronym TARDIS - Time and Relative Dimensions in Space - as if this will help Steven, only to be greeted by Steven's own acronym, IDBI. "I Don't Believe It."

The Doctor orders a scrub and a change of clothes for Steven. He is ready to explore, hoping the evidence of Steven's own eyes will convince him that what they say is true. The Doctor seems particularly excited as they appear to have landed on Earth.

It is the Earth of the recent past. In a small village some distance from the shoreline, a Saxon woman called Edith tends her cooking fire. They are simple folk, but well provided for by the land. She is startled by the sudden arrival of a fellow villager - a man called Eldred. He has come for Edith's husband Wulnoth, the headman of the village. Eldred, too, has seen the strange box on the beach. He believes it may have washed up on shore from a ship. Wulnoth knows the tide will be coming in soon and they must hurry. Forgetting completely about his evening meal, Wulnoth grabs his spear and follows Eldred, much to Edith's consternation.

Steven is looking and feeling better after his clean up. He has new clothes and a cloak, and he has joined the Doctor and Vicki on the beach outside the ship. However, his scepticism is undimmed. Perhaps it is even stronger. The Doctor presents him with a rusted and mud-covered horned helmet. To the Doctor, it is a Viking helmet which indicates they've arrived in 10th or 11th century England. To Steven, it could be a toy left here by a child. The Doctor's uncertainty as to their location keeps Steven from believing this "time travel" story and he is not swayed by the Doctor's claim of a "technical hitch". It's clear to him that, whatever the story, he's not getting home easily with these two.

The group moves over to a large rock nearby where the Doctor flicks pebbles absently while talking. His dark-jewelled ring glitters in the sun. He hopes they can explore further and find a village which might convince the doubting Steven of the truth. Steven asks about the odd exterior design of the TARDIS and gets a terse explanation from the Doctor of the ship's camouflage unit. It is designed to allow the ship to blend in wherever it goes. All the while, the Monk listens to their conversation from hiding on the other side of the rock. Pebbles rain down on his head as he does so. Steven points out that despite this "miraculous" camouflage capability, the ship still looks very like a police box. He finds the "technical hitch" explanation and still disbelieves.

Vicki is tried of all this talking and wants to explore. They must get to the top of the cliff first. Steven advocates climbing, but the Doctor refuses. He plans to walk along the beach until the cliff levels out. Then he will come back to meet the others. Testily, he heads off on his own. Steven, though, refuses to wait and despite Vicki's objections he goes to climb the cliff.

This leaves the TARDIS all alone on the beach...with the Monk. He walks carefully to the ship, making sure he is unobserved. He tries the doors and the lock. He doesn't seem to be trying to enter but to confirm something - as if he's trying to determine whether the object is real. When he presses his ear to the door, he seems to get his answer. And he is wickedly pleased. But he is not pleased when he goes to check his wrist. Whatever he was looking is no longer there. The Monk seems very concerned indeed.

Before long, darkness has gathered and long shadows fill the landscape. The Doctor, still on his own, has found his way to the Saxon village. He arrives at the hut of Edith and Wulnoth but finds no one about. The fire is still burning out front but no one is at home. The Doctor enters the hut and finds all the accoutrements of 11th century English life, confirming his earlier theory. But it is strange that no one is about. The sound of an animal howling nearby snaps out of his reverie and he leaves the hut. But he is no longer alone. Suddenly, he is pinned to the door post by a forked stick which encircles his throat.

The Monk returns to his monastery, on the hill above the village, and lets himself in. The building is very large and quite old, its thatched roof sagging in places. But it seems like home to the Monk. From outside, one can see a light go on in an upper room - a light that snaps on very unlike a guttering candle. And the sounds of dozens of chanting monks drift from the window, voices borne on the wind. However, the entire monastery is empty. From whence come the voices?

Wulnoth and Eldred reach the clifftop. They look down and see only pounding surf below. The tide has returned and whatever was on the beach has likely been smashed against the rocks. They decide to return to the village.

Back in the village, the Doctor's reception has gotten much warmer. It was Edith who trapped him, thinking he was an intruder who meant her harm. But now that he has convinced her he is a harmless traveller, she provides him a place by the fire and a glass of mead. She begs forgiveness for her "harsh welcome" while answering the Doctor's questions about the location of the monastery. The sounds of chanting monks drift through the village. The Doctor is a bit concerned over not linking up with his companions. He walked farther inland than he intended to.

The Doctor takes advantage of Edith's presence to try and ascertain more information about when and where he is. Hiding his lack of knowledge skilfully, he learns that Harold Godwinson has been king for less than a year, making it 1066. The time is late summer and this place is in Northumbria. He wishes Barbara was here to help him with his history, but he manages to remember that King Harold defeated the Norwegian King Hardradda in Northumbria before facing William the Conqueror at Hastings. All of this is still to come, though, and this information should prove to Steven the truth about the TARDIS.

Satisfied by all this deduction, the Doctor sits again by the fire. But suddenly he is up again, agitated. He has heard the voices of the chanting monks slow down and then speed up again, like a recording played at the wrong speed. He summons Edith and peppers her with questions. He learns that the monastery had been abandoned for many years, but a few weeks ago some monks must have moved back in. Although only one of them has ever been seen. In a great hurry, the Doctor takes his leave of her, heading for the monastery. He seems to know more about the monastery than he's revealing and it clearly concerns him. He leaves behind an equally concerned Edith.

Steven and Vicki are lost, having traipsed endlessly through the woods looking for the Doctor. Vicki is tired and forces Steven to stop and rest. However, their rest is short-lived as someone approaches. Steven thinks he should go and talk to the person to try and find out where they are. But Vicki - seasoned by her travels with the Doctor - thinks they should hide and follow the person to determine if it is safe here. Vicki wins out for the moment and Steven crouches with her at the perimeter of a clearing.

The person - a trapper - enters the clearing. He appears to be merely passing through but stops as he sees something shiny on the ground. He picks up the object and stares at it. It is clearly foreign to him. Neither Steven nor Vicki can make out the object in the gloom, but Steven fears it might be something that Vicki dropped. Boldly, he enters the clearing and calls out to the man. Frightened by the sudden appearance of this stranger, the trapper runs. Steven tackles him and a struggle ensues. Vicki tries to stop it, but the melee does not end until the trapper gets the upper hand and hits Steven in the jaw. Steven lets go and the man bolts, running for his life.

Steven is OK, just a little stunned. He is not sorry the man got away, since he was able to steal away the prize the man found. Steven shows the object to Vicki - a modern wristwatch - and smugly asks if she still believes this is 10th century England.

The Doctor's trip to the monastery is a short one. Standing at the door, he can hear the chanting much more clearly. He looks very disturbed by it all. The Doctor tries the door but it is lock. He rattles the handle noisily and then back away.

Inside, the Monk has heard this. Quietly he slides back the wooden bar on the door and retreats.

The Doctor watches as the door falls open. Warily he approaches and enters the monastery. He seems to expect an ambush, checking carefully behind the door as he enters. He sees no one and so continues inside.

Outside, the light in the upper room snaps off, but the chanting continues.

The Doctor traverses the large building, following the sound of the chanting monks. There is no sign of habitation inside the crumbling monastery. The sounds lead him to an alcove covered by a rough cloth. Behind the curtain he finds an old-fashioned gramophone - the very anachronistic source of the chanting. He removes the needle and silence reigns. It is just as he suspected and he is very pleased with himself.

The next morning, the Monk prepares a very anachronistic breakfast for the 11th century: toast from a toaster, bacon and eggs from an electric skillet, and tea from a manufactured pot. He delivers the food through the empty monastery to the Doctor's cell. He is still very pleased with himself for capturing the Doctor.

The Monk makes certain the Doctor is still sleeping before sliding the tray inside the cell. Then he yells to wake the Doctor up. The Monk seems put out when the Doctor is slow to take the fine meal, but the Doctor responds to the taunting by tossing his tea in the Monk's face. Clearly the Doctor will not be a model prisoner.

Wulnoth, Eldred, and some other villagers tramp through the woods, starting their daily hunt early. Nearby, Vicki is awakened by the sound of twigs snapping. She and Steven have slept the night in hiding near the clearing. But when she wakes, Vicki finds herself alone. There is no sign of Steven. She fears the worst, but it soon turns out that Steven was responsible for the sounds she heard. He returns to the clearing bearing a meagre breakfast of blackberries. He has been off foraging.

Vicki jumps up and down to try and warm herself. The two decide they should head back to the TARDIS as soon as possible. They hope that the Doctor will already be there. If not, they'll have to think of another plan. Unbeknownst to Vicki and Steven, their conversation is being overheard by Wulnoth, hiding nearby.

Vicki wonders what time it is and Steven tells her, reading from his new wristwatch. Vicki is tired of Steven's insinuations and suggests that perhaps the Doctor dropped the watch, even though she doesn't recall him ever wearing one. Suddenly they are startled by the sound of a snapping twig. Steven goes to investigate and they are separated.

Eldred emerges and grabs Vicki from behind, holding a long knife at her throat, while Wulnoth and another villager attack Steven and knock him down. The hunters have been quick and stealthy. The strangers are now prisoners, but not to be harmed just yet. Wulnoth wants them taken to the village.

The Monk emerges from the monastery and blinks up into the sunny sky. He goes to check his wristwatch - as he did at the TARDIS the day before - and remembers that it is missing. He curses himself again for his carelessness and climbs up on a nearby rock to look out to sea. But after only a second he clambers hurriedly back down again and sits on the ground, pretending to be absorbed in a scroll he pulls from his pocket.

This is for the benefit of Edith and another Saxon woman who approach up the path. The Monk becomes very pious indeed, noting the intensity of his "meditations". The women apologise for disturbing him and present him with a basket of food. It is rough fare, far rougher than that he can make in his electric skillet, but they don't know that. He accepts it with a gratitude that rings somewhat false and then quickly excuses himself for more prayer and meditation. This works and the women go on their way, leaving the Monk to return to his vantage point and look out to sea again. He uses powerful binoculars but still does not seem to find what he is looking for.

Meanwhile, the Doctor pounds on his cell door and shouts to be released. No one is there to hear him.

The Monk has gone closer to the shore and is now sitting on the breezy cliff top. He waits impatiently for something, doing a bit of snuff to pass the time. Unfortunately, the wind makes this very difficult. By the time he is able to finish, his objective is in sight. Using his binoculars, the Monk spies a Viking ship approaching, its dragon-headed prow unmistakable. He becomes very excited that his wait is finally over.

Steven and Vicki are marched to the village and forced to sit down. Steven is licking his wounds and - perhaps - finally coming to terms with time travel. The Saxons and their village look quite authentic to him. This is clearly no fancy dress party. A bit nervous, Steven decides to try an escape but the Saxon spears suddenly pointed at him convince him to sit back down. Apparently he and Vicki are more popular than he had first thought.

There is serious disagreement among the Saxon as to what should be done about these strangers. Wulnoth thinks they are harmless travellers, but Eldred fears the worst. They have strange clothes and no provisions. They have not travelled far and he believes they are Viking spies. Eldred's fear is strong and he refuses to listen to Wulnoth's entreaties, nor his orders. Eldred snatches up his spear and turns to attack Steven and Vicki.

It is Edith's return which stays him. She sees the strangers and their clothes and asks them if they seek an old man with long white hair. Steven is surprised that she knows the Doctor, as is Wulnoth. She has not had time to tell her husband of the Doctor's visit.

Eldred still refuses to believe and still advocates for the strangers' death. He and Wulnoth are stalemated again until Vicki forces the issue. She is tried of the bickering and wants a decision made, either way. After a moment of thought, Wulnoth decides to let them go. He instructs Edith to get Vicki some provisions for their journey. Relieved, Steven drops the club he had secretly grabbed to defend himself against Eldred.

As Edith wraps some food in a cloth, she tells Vicki about the Doctor's stated plans to visit the monastery. She gives the girl directions and offers to guide them, but Vicki politely refuses. Vicki rejoins Steven and he thanks Edith, Wulnoth, and the others. Chastened by his brush with the past - with tradition - Steven actually returns the villagers' wish that God be with them. Wulnoth orders his villagers into the fields. All go but Eldred, who hesitates, watching after Steven and Vicki suspiciously.

Elsewhere, the Vikings come ashore, climbing the cliffs on ropes and hooks. It is a small scouting party - a handful of men. They have been sent ahead of King Hardradda to learn the lay of the land. Two smaller groups are sent out in opposite directions to survey the territory and to ascertain the strength of the local villages. The Viking leader directs his men to try and remain unseen. If they are detected, they are expected to fight, but surprise would benefit the king much more.

Steven and Vicki reach the monastery and knock boldly on the door. The Monk answers, turning on the fake piety, too think for Steven's liking. He cuts through the platitudes and inquires about their missing friend. The Monk tells them that no stranger has visited for many a day. Vicki enquires whether the other monks may have seen him, throwing the Monk off for a moment. He tries to pass this off too, but when Steven persists, he says he'll go inside and ask "the other monks".

Once they are alone, Steven admits he doesn't believe the Monk for a moment. The Doctor must have come up here and that Monk is lying about it for some reason. He comes up with a plan and tells Vicki to keep quiet while he talks to the Monk.

The Monk - after standing behind the door for a suitable length of time - comes back out with a long face. He does not have any good news from "the other monks". Steven appears to accept this and asks the Monk to keep an eye out for their friend. He asks the Monk to repeat his description, which he does - long white hair, black cloak, strange checked trousers. The Monk then returns inside and locks the door.

Vicki realises the trick immediately. The Monk was never given a description of the Doctor and therefore must have seen him. Steven is certain the Monk is holding the Doctor prisoner in the monastery and is pleased with himself for having forced the Monk's hand. But Vicki is unsure. She believes that the Monk gave himself away deliberately, to trick them into trying to enter the monastery. That's as may be, but Steven knows they have no other choice if they want to find out what's going on. He decides to wait until dark and then try and break into the monastery.

As night falls, Edith is startled from her tent by a noise. Looking around, she sees nothing, but grabs her spear just in case. Just as she steps away from her tent, though, one of the Vikings, a one-eyed giant called Gunnar, descends from a tree and grabs her from behind. The other two - Sven and Ulf - emerge from hiding and enter Edith's tent. Gunnar drags her inside as well.

Back at the monastery, Steven and Vicki begin their search for an unseen entrance.

Wulnoth and Eldred return to the village and find no fire lit in front of Wulnoth's tent. Wulnoth becomes alarmed and shouts for his wife, racing inside the tent. He finds her there, battered and left for dead, her eyes wild and staring. Eldred believes it was the strangers who did this and tries to tell Wulnoth so. The headman's anger and grief burst forth, silencing Eldred. Wulnoth orders him to gather the men of the village. They will avenge this violence with blood.

Meanwhile, Sven, Ulf, and Gunnar move heedlessly through the woods, carrying off the food and drink looted from Edith and Wulnoth.

Wulnoth and one of the women from the village have managed to bring Edith around. She is in pain, but she is lucid. She tells her husband it was the Vikings who attacked her. Eldred arrives with the men and learns this too. All his petty grievances with Wulnoth are erased and the Saxon are united. Their dread and hatred of the Vikings burst forth without words. The men, armed and grim-faced, set out to find and destroy the Viking invaders.

The Vikings' heedless tramp through the woods has left a clear trail, which Wulnoth and the others find quickly. The battle is soon to come.

Drunk on stolen mead and flushed by their own superiority, the three Vikings laugh loudly as they crash through the woods. Their leader's call for stealth seems to have been completely forgotten. The laughter stops abruptly as the Saxon men pour from the woods and attack them. The battle is short but fierce. Several of the Saxons are killed before Eldred and Wulnoth deliver fatal blows to Gunnar, the giant. He crumples, but Eldred has received a deep gash in his arm in the process. Sven and Ulf manage to flee unharmed, but not without killing or wounding most of the other Saxons.

Wulnoth is the only one left unharmed. He gathers Eldred up and decides to take him to the monastery for help as it is closer than the village.

For now, though, all is quiet in the monastery. The Monk passes by one of the many upper-storey windows on his way to the tower. He does not notice Vicki and Steven, who climb inside once he has passed. The two are inside, but are unsure what to do next. Both have different ideas of where to begin their search, but Vicki's choice wins out. Steven follows her.

The Monk starts up his recording of chanting for the evening and resets the trap in the alcove. Clearly he is expecting visitors tonight.

Wulnoth is now forced to drag Eldred, so weak has he become. He stumbles and both men fall. Eldred seems insensible but Wulnoth is determined not to lose his right hand man to the Vikings.

Steven and Vicki continue their search, glad of the chanting to keep "the monks" occupied. However, the Monk observes them as they go, appearing ready to spring his trap. Suddenly he is distracted by the sound of knocking at the monastery door. He hesitates for a moment and then reluctantly goes to answer it.

Steven and Vicki locate the gramophone playing the chanting and are dumbstruck. Nothing is as it appears here. Unbeknownst to them, they escape the Doctor's fate as the Monk is not there to activate the trap. They leave the alcove and begin to search the nearby rooms, peering in the window openings.

At last, Steven finds what he's certain is the Doctor. He is lying on a straw pallet, his cloak covering him. But it is clearly the Doctor's cloak. Steven uses a penknife to pick the lock.

The Monk answers the door just as Wulnoth is ready to batter it down. The Monk cannot refuse Wulnoth's request for help without blowing his cover and so admits the two men. Not that Wulnoth would have taken no for an answer.

Steven succeeds in picking the lock and he and Vicki enter the cell. Vicki tries to wake the Doctor, but finds that the only thing beneath the cloak is a pile of furs.

The Monk leads Wulnoth to a small cubicle where Eldred can rest. The Monk then goes to fetch some medical supplies.

Steven and Vicki realise that the Doctor must have escaped from the cell using some means other than the door. Otherwise it wouldn't have been locked. The only logical explanation is a secret passage somewhere in the room. Steven is hard-pressed to credit this cliché, but nonetheless joins Vicki in searching.

After some time, Vicki detects a loose stone in one wall. Steven finds and opens a secret door, impressed at Vicki's cleverness. Together they enter the rough-hewn passage, closing the door behind them.

On his way to fetch medicine, the Monk decides to stop and check on his prisoner. However, the door is open and a quick search reveals no one inside. He is confused and frustrated, not sure where or how to begin looking for the Doctor. However, he is interrupted by an insistent shout from Wulnoth and must return to his original task.

The secret passage weaves its way through gnarled tree roots and damp earth. Steven and Vicki are tired but must keep going. There's no sign of the Doctor yet.

But the Doctor has indeed escaped via the passage and has made his way back to the Saxon village. He has returned to Edith's tent, but it is a much more subdued Edith who now sits with the Doctor. From her, he learns that his friends have been looking for him and went up to the monastery. He is somewhat distressed that they didn't wait for him at the TARDIS and decides to go after them shortly.

The Doctor also learns of the arrival of the Vikings. He mistakenly believes it is a fleet of ships and tries to cover his foreknowledge when Edith tells him it was only a small scouting party. But she realises what he is saying and the Doctor is forced to admit that a full invasion fleet is on its way. The Doctor mutters something about the suspicious nature of the Monk's presence here at this pivotal moment in history and then assures Edith that the Viking invasion will land well south of here and be defeated by King Harold. He seems unconcerned about giving away future events when he mutters aloud about the Battle of Hastings within Edith's hearing. As he goes off, Edith watches after him, very concerned indeed.

Steven and Vicki finally emerge from the passage in a small clearing in the woods. There is still no sign of the Doctor. They must find him. Steven now fully accepts that the TARDIS is a time machine and that this is 11th century England, but the wristwatch and the gramophone are anomalies that must be explained. They must be connected with the Monk. The sooner Steven and Vicki find the Doctor, the sooner they can find an answer to this mystery.

The Monk takes some antibiotic tablets from a 20th century first aid box and gives them to Eldred. He tells Wulnoth they are herbs. The Monk sends Wulnoth to put his sword outside, claiming this to be a place of peace. But as soon as he's gone, the Monk questions Eldred about the Vikings. He believes that the main Viking fleet will arrive within 2 days and seems very pleased. He is "right on schedule".

Wulnoth insists that Eldred must stay here and recover, but he promises to send Edith to help and he himself will call regularly. The Monk becomes alarmed at the growing number of visitors to his monastery and tries to protest. Of course, he cannot refuse without blowing his cover and so accepts. Wulnoth heads back to the village gratefully.

The survivors of the Viking party - Sven and Ulf - are still in the woods near the village. Both fear for their lives, certain that every Saxon for miles will be searching for them. Sven wishes to try and complete their scouting mission, moving further south, but Ulf thinks this an invitation to death. He prefers to hide until the main fleet arrives and rejoin their people when their numbers are greater. This seeming cowardice angers Sven and a fight ensues. However, Ulf persists and the plan begins to sound better. Ulf suggests the monastery as the ideal hiding place and the monks there will be perfect hostages. Sven still believes this is a craven plan on Ulf's part, but the logic of staying alive appeals enough to him that he agrees.

Left alone for a moment, the Monk decides to check on the progress of his plan. He has an elaborate checklist that begins with his arrival in Northumbria and ends with his meeting King Harold! Several items are already ticked off including "position atomic cannon". He ticks off "sight Vikings" and is very pleased with his progress. The next step is the lighting of beacon fires, presumably to guide the Viking fleet in to land. It seems very clear that the Monk is planning to aid the Vikings in their invasion. But, in order to get the fires lit, he plans to get the villagers' help somehow.

He works with a map on top of an old stone sarcophagus to plot the exact location of the fires, but he is interrupted by yet another knock on the door. Highly annoyed, the Monk stows all of his papers inside the sarcophagus and goes to answer the door.

At first there appears to be no one about, fuelling the Monk's anger. But when he closes the door and the knocking comes again, he is more concerned than angry. Again no one is waiting when he opens the door and he stops out cautiously to investigate. Suddenly the Doctor appears from hiding, poking a stick into the Monk's back as if it were a gun. He leads the Monk back inside, a determined look on his face.

The Doctor closes and locks the door, making certain the Monk doesn't turn around and see the stick. The Monk is chagrined at the Doctor's reappearance and the Doctor chalks it up to curiosity. He has several questions to which the Monk will provide answers.

Steven and Vicki have returned to the clifftop above the beach where the TARDIS landed. But instead of seeing the familiar blue police box, they see only swirling water. The tide has come in and swamped the ship. Steven wonders if the Doctor mightn't have returned and moved the ship to avoid the tide, but as Vicki knows that would be even more disastrous than the water. If he left here, he could never return.

Instead of sitting around speculating on what might have happened, Steven suggests a course of action: return to the monastery. Vicki, despondent over the possible loss of the TARDIS, is reluctant to move at first. But Steven notices something in the bushes which draws both of their interest. It is a very futuristic looking gun, like a miniature cannon. It has been placed there deliberately - by the Monk they speculate - and pointed out to sea. This find galvanises them into action and they hurry off back to the monastery.

The Doctor forces the Monk deeper into the monastery, but it becomes clear that the Monk is leading him round in circles, playing for time. The Monk discovers the Doctor's ruse with the stick, but the Doctor assures him he will use the stick if necessary! Their banter sounds more like that of old friends than adversaries. The Doctor demands to know the Monk's plans, but is interrupted by a knock at the door.

The Doctor wishes to ignore the knock, but the Monk says he must go. Otherwise whoever is outside might get suspicious. The Doctor accepts this but is still suspicious, especially when the Monk suggests the Doctor put on a Monk's habit to answer the door himself. Reluctantly, the Doctor agrees to the disguise but reminds the shifty Monk that he is still armed... and determined.

A short time later, suitably dressed, the Doctor himself opens the door while the Monk watches. A sword comes through the gap and rests at the Doctor's throat. On the other end is Sven, the Viking. He disarms the indignant Doctor and he and Ulf enter. The Monk is now nowhere to be seen - they do not even know he is there. The Doctor is thrown back into his cell as a hostage and guarded by Sven. Ulf will find and give terms to "the other monks". They will all surrender or the Doctor will die.

However, Ulf has difficulty finding any other monks at all. After a while, he enters the sarcophagus chamber and is knocked unconscious by the Monk. Lamenting yet another kink in his otherwise perfect plan, the Monk ties Ulf up.

Steven and Vicki are having a bit of trouble finding the entrance to the secret passage in the woods. It all looks different in daylight. Once they find it, Vicki is reluctant to slog back through the passage, but she knows it is the only safe way into the monastery.

Sven awakes from a short nap to check on his prisoner. He is concerned about Ulf's extended absence, but becomes even more alarmed when he doesn't see the Doctor in his cell. Instead, the door to the secret passage stands wide open. He hurries inside, fearing what he will find. However, when Sven peers into the passage, the Doctor emerges from his hiding place behind the door and knocks Sven out with a blow to the head. The Doctor hurries off, wondering what took Sven so long to come in!

Whilst the Doctor has been incarcerated, the Monk has been busy. He has gone to the village, calling on Wulnoth and Edith. He has a favour to ask of the villagers - to prepare beacon fires on the clifftops. Wulnoth and Edith are immediately concerned as Edith has shared with her husband the Doctor's warnings of a Viking invasion. The Monk invents a story about building materials arriving by sea and Wulnoth agrees to prepare the fires. However, when the Monk leaves - to "tend to Eldred" - Wulnoth expresses his fear to his wife. He is suspicious indeed of this Monk and his beacon fires and has no intention of preparing them.

Steven and Vicki arrive in the cell and find Sven still unconscious. Vicki is concerned at what this might mean, but Steven assures her they haven't time to puzzle it out. He grabs up the Viking's sword before he and Vicki head off in search of... whatever it is they might find.

The Monk returns and stops to speak with Ulf, still tied and gagged. Chattily, he tells Ulf about the beacon fires for his fleet, unaware that the Doctor is free and is nearby listening. The Doctor places a sword under the Monk's chin and tries to force him to explain his plan. Is he helping the Vikings or not?

Steven and Vicki's search has led them to the sarcophagus chamber where the Monk was working earlier. They despair of finding anything here until Vicki discovers a power cable snaking across the floor. They follow it to the rear of the sarcophagus, where two doors are incongruously inset. The cable disappears inside.

Intrigued, Steven and Vicki decide to enter, but they are unprepared for what they find. The doors lead not into a stone box but into a giant, brightly-lit, futuristic control room. It is very familiar, as is the hum that resonates all around. It is a TARDIS.

Under pressure from the Doctor, the Monk divulges part of his plan. The beacon fires are indeed to draw King Hardradda and his fleet to shore. But not to help them conquer Britain. Instead, he plans to destroy the entire fleet!

Vicki and Steven are still quite stunned by their discovery of the Monk's TARDIS. It is not exactly like the Doctor's, though. The console sits on a small dais and one corner of the rooms gives way to a museum-like collection of historical artefacts from many times and places. Steven and Vicki hurry over to investigate.

Steven locates some small, futuristic rockets - neutron grenades - which would fit the cannon they saw on the clifftop. It would be more than adequate to sink a passing ship. But why would the Monk want to do that? Vicki thinks she may have found a clue in a small diary she's discovered. The Monk has been meddling his way throughout Earth's history, teaching DaVinci about powered flight and using time travel to collect a fortune in compound interest from a bank.

The Doctor has reached the same conclusion about the Monk, berating him for breaking the "golden rule of space and time travel": never, never interfere with the course of history. The Monk tires to tell the Doctor of the gleeful fun he's had while travelling through time, such as providing anti-gravity machines to help build Stonehenge, but the Doctor is incensed.

The Monk is most pleased with his current plan to change history - a master plan to end all master plans. By destroying Hardradda's fleet, the Monk will spare King Harold the battle. Thus he and his men will be fresh and rested for the more important Battle of Hastings still to come. William the Conqueror will be easily defeated, ending the Norman threat to Britain. The Monk thinks he has gotten through to the Doctor and convinced him of the plan's merits, but it quickly becomes clear that is not the case. The Doctor is very glad indeed that he has arrived in time to prevent this "disgusting exhibition".

The Monk realises he's said too much but denies that the Doctor can stop him. The Doctor thinks otherwise and forces the Monk to show him his time machine.

Sven has finally awoke, with a splitting headache. He calls out for Ulf as he searches for him. He is seen by Eldred, stunned by the sight of Vikings running free in the monastery.

Sven finds and unties an angry Ulf. He wishes to leave this place and rejoin their comrades, but Ulf's pride has been wounded. He wants to stay and teach the monks a lesson. He also thinks there may be treasure hidden in the monastery. This may be a long shot, but it is enough to convince Sven. They will stay.

The Monk shows off the exterior of his time machine - a perfect Saxon sarcophagus - with considerable pride. He needles the Doctor about his faulty camouflage unit, but does not get a rise. The Monk goes on and on about the extent of his planning and preparation for this adventure. He is very proud of himself indeed. But the Doctor easily deflates him with stinging words and the Monk quietly leads the way inside his ship.

Eldred, desperate to warn his fellow villagers about the Vikings in the monastery, ignores his wounds and sneaks outside. Once in the clear, he hurries to the village.

Steven and Vicki have found the Monk's checklist for this adventure. It seems to answer for them all the mysteries they've discovered here, but there is still the question of why he would want to affect history this way.

The Doctor arrives with the Monk, that same question on his mind as well. There is a brief, joyous reunion between the Doctor and his friends. The Doctor examines the Monk's ship, noting that it is a Mark IV. He compares it to the TARDIS while Vicki tries to tell him about the tide that has engulfed their ship. The Doctor is unconcerned as the water cannot affect the TARDIS. He congratulates the Monk on his "splendid machine", noting several advancements over his. The Doctor confirms for Steven that he and the Monk come from the same place, but that the Doctor is approximately 50 years earlier.

But all this talk does not distract the Doctor from his main goal - to find out why the Monk is attempting to change history here and now. The Monk says he wants to improve things in this time. He feels that Harold could be a good king if he were to live. He could keep peace in Europe and help the people prosper. With some hints and tips from the Monk himself, mankind could leap into the jet age by 1320 and have television in the time of Shakespeare. But to do this he must kill all the Vikings.

The Doctor is irate at this irresponsible meddling, but as he searches for a course of action, he accidentally allows the Monk a clear escape path to the door, which he takes. Vicki sees him flee and they all follow him.

The Monk runs straight into the hands of Sven and Ulf and it looks as if the jig is up. Thinking quickly, the Monk swears allegiance to King Hardradda and sets the two Vikings on the Doctor and his friends, their "true enemies".

In the Saxon village, Wulnoth has gathered his men and is whipping them into a frenzy against the Vikings. He and Edith believe the Doctor and fear that a Viking invasion is imminent. They tell the men that the Monk is a Viking spy planning to use the beacon fires to bring the Vikings down upon them. Into the mob comes Eldred, pale, worn, and glassy-eyed. He tells them of the Vikings hiding in the monastery and the men react with unfettered anger. They head off, armed and furious, to deal with the Vikings and their agent.

The Monk has managed to convince Sven and Ulf that he is on their side. He has talked them into lugging the heavy box of neutron grenades to the clifftop, backbreaking work he's glad not to have to do. He tells the Vikings that the strange objects are "charms" to lead their ships to sheltered water and laughs at their gullibility.

Meanwhile, Steven, Vicki and the Doctor have been bound hand and foot. Steven returns - hopping on his bound feet - from a scouting trip. He has not been able to find anything sharp enough to cut the ropes. It appears to Vicki that the Monk will succeed in his plan to change history. This is news to Steven as he's certain in his memory that William the Conqueror won at Hastings. But the perils of time travel soon become clear to him. If the Monk succeeds, all history from here forward will be changed, and their lives along with it. It is a very sobering thought.

Vicki nudges the Doctor, who appears to have fallen asleep while in captivity. But he is very much awake and thinking through the situation. He has come to the same desperate conclusion as the others - the meddling Monk must be stopped!

Wulnoth, Edith, and the men of the village move silently through the woods toward the monastery. Surprise - and numbers - will be on their side when they find the Vikings.

The Monk exhorts Sven and Ulf to hurry, opening the monastery door for them to exit. But they barely step outside before the Saxons are upon them, yelling in rage. The Vikings drop the box and retreat into the monastery, the entire group of Saxons following them. The Monk manages to stay out of sight behind the door and heads outside at a run as soon as the Saxons are out of sight.

But Sven and Ulf know they stand a better chance out in the open and find a way to return to the doorway. They burst through into the woods - not far behind the Monk - followed hotly by the Saxon men.

Luckily for the Doctor and his friends, Edith has not joined in the pursuit, remaining instead to search the monastery. She has found and freed the captives, thanking the Doctor for alerting them to the Viking threat. The Doctor is worried when he learns that the Monk has not been caught. He knows the wily fellow still has some tricks up his sleeve. Edith returns to the village whilst the Doctor tends to some "business" here in the monastery.

Vicki hopes they're headed back to the TARDIS, but that is not the case. The Doctor needs to stop the Monk once and for all. His first weapon paper and pen.

Sven and Ulf race for freedom through the woods. They are now outpacing the Monk but he calls them back when they reach a clearing. He points out an old well nearby in which they can hide. But it is a trick and the Monk runs off without them. Sven and Ulf return to the clearing when they discover there is no well and it is there that the Saxons catch up with and capture the renegade Vikings.

The Doctor, meanwhile, has been hard at work inside the Monk's time machine. He has managed to pry loose a clear plastic box filled with wires and connectors. The box is tied to the underside of the control console by a cable and the Doctor treats it very gently indeed. Steven arrives with a requested ball of string which the Doctor carefully ties to the box, despite Vicki's interference.

The Doctor backs out of the machine, forcing Steven and Vicki ahead of him. It is a very dangerous business and he ignores their questions to concentrate on the task at hand. He plays out the string as he goes. Once outside, he pulls in the slack on the string and eventually reveals that he has removed the box from the console, cable and all. He is very pleased with himself but will not explain why.

Steven and Vicki cannot see what this has accomplished, but the Doctor is certain he's put paid to the Monk's meddling. He leaves a note for the Monk on top of the sarcophagus, despite Vicki's interest in opening it, and urges his companions back to the TARDIS at last.

The Monk, meanwhile, is still running for his life.

The Doctor, Steven, and Vicki reach the cliff overlooking the TARDIS and find it safe and sound. The water has retreated and they can now climb down the cliff to the ship. They must hurry as the Viking fleet will soon arrive. Steven is pleased to learn that history is safe and he even seems pleased with the idea of being a time traveller. The group heads off to find an easy way down the cliff.

The Monk has managed to elude his pursuers and return to the monastery. Worn out and gasping for breath, he enters. All is quiet inside and he is sure the Doctor has left this place for good. His plans well and truly thwarted, he decides that he himself had better be on his way as well.

But the Monk becomes suspicious when he finds the Doctor's note. In it the Doctor claims to have ended his time meddling - which the Monk does not believe for a moment - and says that one day he might return "to release him". This is a very troubling phrase and the Monk's bravado collapses. He goes to his ship to investigate.

To his horror, the interior dimensions of the ship have been reduced to those of the outside, leaving the ship looking like a doll's house, everything in miniature. There is no way the Monk can even get inside, let alone fly it. He is marooned in 1066!

The Monk screams out his anger against the Doctor, but knows he can do nothing else. He slumps down on some stairs, stranded, alone and forlorn.