A spaceship drifts through space, tracked by UNIT operatives. At first they think it is a comet. But when it changes course, they realize it is coming to Earth. Aboard the ship, amorphous tentacled aliens prepare for their arrival.

In UNIT HQ, a pompous MP, Chinn, goes through UNIT's top secret files, watched carefully by the Brigadier. As head of a Committee of Inquiry, he is annoyed that he can find no information on the Doctor. As he fumes about the identity of the mysterious alien, the Doctor swoops into the office, resplendent in his usual suit and cape.

Bill Filer meets with Jo Grant. Filer has arrived from Washington to help UNIT deal with the Master.

The Doctor quickly loses patience with Chinn. As they argue, Jo arrives with Filer. The Doctor tells Filer the Master has probably left Earth by now. Filer is ready to present Washington's report on the Master but gets into an argument with Chinn about security.

They are interrupted by alarm bells. They quickly meet in the radar room and confirm that the approaching object is not a nuclear missile, but a spaceship. The Doctor quickly calculates that it will land on the southeast coast of England.

On the coast, a rustic hobo scrabbles off of a ship and onto a bicycle.

Chinn reports that he's been given authority to attack the spaceship. He quickly organizes missile batteries, to the Doctor's annoyance. UNIT confirms the Doctor's calculations and that reports freak snow storms are hitting the landing site.

Chinn orders the missile launch. But the ship vanishes before they can hit. The Doctor pushes Chinn to abort the missiles at the last second before they impact the ground.

The spaceship crashes on the coast, near the Nuton Power Complex, which provides much of Britain's power. The blast wave knocks the rustic wanderer into a river.

Chinn, now vested with emergency powers, demands an all-out attack, thinking the alien hostile. He kicks Filer out of UNIT HQ.

The rustic man finds the crashed ship and rushes up to it. A hatch in the back opens and tentacles reaches out and drags him in. It proceeds to analyze him.

Filer switches his radio to listen in on the UNIT broadcasts. He quickly drives to the crash site, just ahead of the army. He is grabbed by a tentacle.

Sir George Hardiman and Professor Winser from the Nuton complex come to UNIT's mobile HQ, concerned about the effects of a battle nearby. Chinn is insistent on the need for an artillery strike. The Doctor points out that the ship has buried itself deep in the ground. As they talk, they begin to pick up tranmissions from the ship that sound like a heartbeat.

The ship decides Filer is too intelligent to be destroyed and keeps him prisoner.

A voice comes in from the transmission. It is from Axos, pleading for help. Chinn still wants to attack, but the Doctor leads them out to the ship, leaving Jo behind. The hatch opens and they walk into the ship.

Benton summons Yates to investigate a body and an abandoned car. They find the tramp's body, horribly wasted. It collapses and vanishes on Yates' touch. While they investigate, Jo sneaks past them.

The Doctor, Hardiman, Winser, the Brigadier and Chinn walk through Axos, which is like no ship they've ever seen. It's organic with transparent walls embedded with eyes. When they spot the Doctor, he's enveloped in a field that paralyzes him. Axos realizes he is an alien before letting him go.

Filer wakes up and finds himself held fast by claws. He calls for help and sees he is not alone. The Master stands next to him.

Jo comes aboard and hears Bill's voice. She begins to look for him.

The Doctor finally finds the inhabitants of the ship, a family of handsome, gold-skinned humanoids. The male slowly begins to speak. He tells them they have come from the far rim of the Galaxy, from a planet crippled by solar flares. Axos is all that remains of their civilization -- an organic ship grown from a single cell. They ask to stay so that they can replenish their energy and offer Axonite as payment.

They explain that Axonite can absorb and transmit all forms of energy and matter (prompting the Doctor to ask how they were crippled by the radiation of the solar flare). Axonite is a thinking molecule that can change shape. He demonstrates it by using Axonite to grow a frog to massive size. Axonite could potentially solve all the worlds hunger problems.

The doctor hears Jo's screams and rushes off. Chinn stays behind and begins scheming to get rid of the UNIT interference.

The Doctor finds Jo unconscious with a humanoid Axon standing over her. she tells the Doctor and Brigadier what happened and the Axon says it must have been a hallucination caused by being near the ship's power source. The Doctor seems to accept this explanation.

Filer gets his gun free and starts shooting the tentacles. The Master instructs him to shoot a nearby ganglion that controls that section of Axos. Ge does and they are able to break free.

Chinn reports on the events to the Minister. He reports that he is having problems with UNIT and asks for Special Powers.

The Doctor tells Winser and Hardiman to wait on accepting the Axonite until they've analyzed it.

Filer and the Master are caught by the Axons. They take Filer to the replication center.

Chinn tells the Axons to give the British government sole distribution rights on Axonite. They agree, provided he distributes its worldwide, and give him a sample for analysis. After he leaves, the Axonites revert to amorphous blobs.

Chinn confronts the Brigadier, but Lethbridge-Stewart forces him to turn over the Axonite. However, when they leave Axos, they find the regular army has taken over the operation and arrested all of the UNIT men. Chinn takes the Axonite back and has Captain Harker imprison the Brigadier to prevent him contacting Geneva.

The Doctor wonders why Axos is foisting Axonite on them. He asks Jo to repeat her story, telling her he believed it all along. They talk about the tramp and Filer's car. They worry that Filer has also been killed. Jo wants to force Axos to let them search but Chinn refuses to allow it -- as far as he is concerned, 'the man has ceased to exist!"

Inside Axos, Filer is enveloped in swirling lights. He watches helplessly as a copy of himself appears.

Chinn has Jo imprisoned with UNIT but Winser gets him to let the Doctor help with their research.

The Axon talks to the Master, thanking him for briniging them to Earth as he promised. They must, however, activate their nutrition cycle within 72 hours and Axonite must encircle the world by then. The Master tells them this will only happen if the people of Earth find out about their deal with the British government. The Axon reminds him that their deal was for the death of the Doctor in exchange for his own life. But they confront him with the fact that the Doctor is also a Time Lord. After Filer is brought back, the Axon reminds the Master that no one is irepelacable.

The Doctor is brought to Winser's massive lab with its particle accelerator. inser explains that they are trying to accelerate particle beyond the speed of light to enable time travel.

In the center of Axos, a massive eye dangles from the ceiling. It instructs the Filer clone to find and bring back the Doctor.

The Doctor hints to Winser about his own experience of time travel, hoping to repair his TARDIS using the equipment. The arrogant Winser seems skeptical.

Filer wakes to find himself bound by claws again. This time, he slowly ease himself out of their clutch.

The Doctor and Winser begin to argue. The Doctor thinks that if they accelerate the Axonite in the accelerator, it will analyze itself, if what the Axons say about it is true. Winser doesn't want to risk his expensive equipment and suggests more mundane experiments, which frustrates the Doctor.

The Master tells Axos he knows Earth very well and he is the only one who can get Axonite distributed within 72 hours. Axos agrees but refuses to turn over the Master's TARDIS. It does agree to turn over his laser gun.

The Master hurries out. As he does, Axos realizes that Filer has escapesd and raises the alarm. The Master emerges from Axos and blasts down the soldier guarding the entrance. As he leaves, Filer also escapes.

Winser and the Doctor find that Axonite resists analysis. The Doctor suggests they use the nuclear reactor to power a particle accelerator in his TARDIS. Winser leaves to get permission.

The Master jumps from a bridge onto an army truck and hypnotizes the driver.

The Filer replica comes to the accelerator and tries to bring the Doctor back to Axos. The Doctor isn't fooled but the replica is immune to his Venusian akido. The real Filer arrives and the replica knocks the Doctor out. Filer shoots the replica to no effect. They begin to wrestle. The Doctor wakes up in the middle and the replica falls into the particle accelerator and is destroyed.

The Master has the hypnotized driver take the Doctor's TARDIS.

The Doctor and Filer fill Jo and the Brigadier in on Axos and the Master. Filer explains that Axos is just a scavenger and they must to stop Chinn. But they are interrupted by Harker who takes Filer's gun. He had the room bugged.

The Master goes to the radio operator, hypnotizes him and has him send a message to the UN explaining the situation.

The Doctor begins to experiment, leaving a recording for Winser. He puts the Axonite in the accelerator. He switches on the accelerator and pushes the particles past the speed of light.

Aboard Axos, there is chaos. Light blazes through as the Axons stumble around in confusion. The nutrition cycle has been activated early.

As alarm bells ring through the Nuton Complex, Harker goes in to check on the prisoners. They jump him. The Brigadier goes to UNIT HQ while sending Jo and Filer after the Doctor. They find him in the lab with the Axonite bubbling over, absorbing the entire output of the nuclear reactor and using it grow.

Winser arrives, enraged. He switches off the reactor and tries to open the accelerator. But he is killed and absorbed. The Doctor realizes that the ship, the Axons and Axonite are all one vast creature. He's prematurely activated it and the entire world is in danger.

Filer tries to attack the Axons but is knocked out by a blast from a tentacle. The Axons surround Jo and the Doctor, who go into a trance. The Axons then transform back into gold-skinned humanoids and lead the two away.

The Brigadier calls Geneva to alert them to Chinn's deal but they have already received a similar message from UNIT HQ. As the Brigadier fumes about the security leak, Harker comes back to arrest him. But the Brigadier tells him to call his HQ for new orders.

Chinn and Hardimanm rush into the lab where the find the Axon male. He tells them Winser was interfering with the structure of Axonite and released a blast of radiation that killed him. They tried to help but it was too late. He threatens to cancel the agreement if any more experiments are done.

Jo and the Doctor are bound aboard Axos.

Harker tries to advise Chinn of his new orders, but Chinn ignores him. Hardimann asks about the others and the Axon says the only man he found was the comatose Filer. He returns to his ship. The Brigadier and his men arrive and take Filer to the medical wing.

Axos brings the Doctor and Jo into a chamber and explains that it merely accelerates the natural death of things. Axonite is bait for human greed. Once it encircles the globe, they will suck the Earth dry of all living matter and all energy.

The Brigadier tells Chinn things have changed. Chinn blusters and fumes but the Brigadier orders Harker to set his men loose to find Jo and the Doctor.

The Doctor thinks that Chinn has done the right thing for once. For now, Axonite is confined to Britain.

Chinn is contacted by the Minister, angry about the security leak. The UN is demanding the immediate worldwide distribution of Axonite. He tells Chinn to either get the Axonite distributed or sign his resignation. Chinn immediately calls up the air transport liason.

Filer begins to talk in his coma, urging them not to distribute Axonite.

The TARDIS is brought to the Nuton complex. Benton reports in to a general for a surprise inspection. After the soldiers leave, the general is revealed to be the Master. The Master quickly breaks into the Doctor's TARDIS and finds the TARDIS console in pieces, with wires and components strewn about from the Doctor's desperate attempts at repair.

Axos interrogates the Doctor about time travel, using pain and flashes of light. At first, the Doctor denies being a Time Lord. But Axos tells him it can remove the blocks from his memory. Axos want to be free to move in time to drain other worlds. When the Doctor refuses to cooperate, Axos arranges for Jo to age to death before his eyes. He agrees to cooperate.

The Brigadier tells Chinn he wants to delay Axonite distribution until they've heard from the Doctor. Chinn proclaims the Doctor a charlatan who will never be seen again.

The Doctor thinks the time equations and Axos reads them. It is alarmed to see that the power requirements are enormous. It is beyond Axos' capability but with the Nuton Complex's output, Axos could do it. It boasts that it can just walk in and take the power.

Chinn is rapidly arranging the transport of Axonite all over the globe. The Axonite male receives orders to go into the reactor and departs.

Filer awakes and tells the Brigadier what he knows. The Brigadier heads out to alert Chinn, followed by Filer.

The Axonite male has begun reverting to alien form when he encounters the Brigadier. He continues on to the power complex. UNIT soldiers open fire but are killed by its tentacles.

The Brigadier alerts Hardiman to the danger. Hardiman finds that the reactor is reading strangely.

The Master has repaired the Doctor's TARDIS but is unable to get it to work. He hits on the idea of tapping the nuclear reactor. But when he goes out, he is spotted by Mike Yates. The Brigadier quickly surrounds and arrests the Master.

The power begins to build in the reactor toward a critical explosion. The Master tells them that he can stop Axos -- in exchange for his freedom. The Brigadier reluctantly agrees. The Master suggests linking the TARDIS to the accelerator so that it can store up the output to the reactor, then throw it back in so that Axos receives a massive blast of energy rather than a slow buildup.

Filer arrives and tries to arrest the Master but the Brigadier forces him to let him go.

Aboard Axos, the power slowly builds up. But suddenly it levels off and begins to drop. The Doctor manages to free himself and goes in search of Jo.

Hardiman continues to feed the power through to the Master, nervous about blowing the cables.

The Doctor frees Jo and they begin to make their way out of Axos.

Aboard Axos, it is complete chaos. Axonites stumble around, light and noise fill the air and claws flail at the Doctor and Jo. Jo is overwhelmed by the assault on her senses. The Doctor forces her to focus by asking her math questions. They manage to stumble out of the ship and hurry back to the Nuton Complex.

The Master gloats over this success and gets ready to leave. But the Brigadier forces him to stay until they know what he's done. Hardiman realizes that the power surge has not destroyed Axos and it is feeding the power right back at them.

Hardimann has the staff and UNIT evacuate while he prepares to break the connection. He puts on a mask and gloves and steps into the accelerator. The Brigadier and his men watch from the gallery as Hardimann works. He disconnects it but is electrocuted and killed. When the soldiers rush out to help him, the Master tries to bolt into the TARDIS but is stopped by Filer. He tries the doors, but runs into Jo and the Doctor.

The Doctor tells them that the claw of Axos are already deeply imbeeded in the Earth's carcas. Unless they stop it, it will consume the world. The Doctor begins to plan his next move. He asks Filer to hand over the Master since he needs his help.

Yates sets watch over Axos and reports in to the Brigadier. Chinn reappears, now eager to do something about Axonite before he gets the blame.

Jo talks to Filer, who is disappointed and nervous about what the Doctor and the Master are planning. He sees them scavenging components and ignoring the techs and wonders why they are doing it.

The Doctor and the Master return to the TARDIS and the Doctor offers an alliance, claiming Axos is unstoppable. He tells him they either escape together or die together. He needs the Master's help since he can't remember how to make the TARDIS work. The Master agrees to help and tells him to cannibalize the accelerator to fix the dematerialization circuit. The Doctor heads out to calculate coordinates but removes the dimensional stabilizer to keep the Master honest.

Axos realizes that Axonite has encircled the globe. It begins its nutrition cycle, absorbing energy from all over the world. As it does, it emerges from the ground. The Brigadier orders Yates and Benton to evacuate but they are attacked by Axons en route. The Axons stop the jeep by knocking over a tree and jump aboard. Benton fights with them and eventually primes a grenade while he and Yates jump out. The Axon is destroyed with the jeep.

The Doctor has Jo calculate some course coordinates, which arouses Filer's suspicions. The Doctor then admits that he is leaving them. Filer draw his gun but the Doctor blasts it out of his hand with the Master's laser. The Doctor bids them farewell.

The Doctor replaces the missing component and takes off. Yates reports they are being over-run by Axons. They take shelter behind the computer banks.

The TARDIS lands inside Axos. The Doctor offers a deal to Axos. He will give them time travel if they attack the High Council of the Time Lords. They will do this by linking Axos to the TARDIS' drive systems.

The Master tries to go back to his TARDIS but is stopped by Axos who wants him to wait until the link is complete.

The Axons burn through the doors of the accelerator room. A spark flies through and burns out the light accelerator, forcing the accelerator to build up to an explosion.

The Doctor is plugging Axos into the console when the Master realizes that the coordinates are set in a time loop. He runs out and alerts Axos, who is distracted by problems with the nutrition cycle. He manages to get into his TARDIS and escape. The Doctor activates the console but it struggles with the load.

The Axonites burst into the accelerator room. The UNIT soldiers put up a fierce resistance but they Axons are immune to their guns and grenades. Several soldiers are killed as the aliens inexorably close in on the Brigadier, Jo and Filer.

Finally, the TARDIS activates. Axos dematerializes along with all the Axonites. Axos tells the Doctor he is stuck in the time loop with them. But the Doctor manages to take off again, leaving Axos trapped.

With the accelerator building, the UNIT people evacuate just as the Doctor returns. The Doctor emerges to find the building collapsing. He quickly jumps back into the TARDIS and takes offf.

The UNIT people get a minimum safe distance and watch as the complex explodes. They hurry back to investigate the wreckage just as the TARDIS returns.

The Doctor explains that a time loop sends one passing through the same points in time, but the humans can't grasp the concept. The Doctor isn't sure what happened to the Master.