As Ace is dragged into the cell, she refuses to tell her captors anything until she gets a lawyer. She complains about her rough treatment, but the only response she gets from the robot constable is that her trial will take place in approximately 3.45 hours. She realises she’s not alone in the cell, but her fellow prisoner, a young woman, claims that she doesn’t have a name. Ace asks if she knows a way to escape, but the woman tells her anyone who tries forfeits their right to a trial. Ace wonders if the woman has been caught before, but the woman doesn’t know because the punishment for those found guilty is to have all their memories wiped before being sent on their way. Ace assures her they’re going to be OK, but the woman’s trial is due to take place very shortly. Ace examines the lock on the door and is impressed by the technology, but she’s good at taking things apart - which is why she ended up here in the first place.

The other woman has been accused of stealing, but she insists the constables are wrong. Ace believes her because she has an innocent face. That was a mistake, because the woman is a lot more than just a thief. She’s also a liar, a temptress and even a killer. In fact, she’s killed thousands, maybe even millions of people without a second thought. And Ace was one of the first to die…

Eventually Ace works out a way to open the cell door and the woman agrees to follow her, admitting to herself that she’s always been easily led by strong personalities. It’s part of who she is and her sister Amy is exactly the same, both of them malleable like clay. Amy isn’t really her sister, of course. They’re both artificial constructs created by the Grace. It’s difficult to describe the Grace to anyone who can’t perceive their dimensions. They exist outside time and space and are mostly occupied with higher matters, such as keeping the Universe in order. When they do need to become involved in this ‘reality’ there’s not much to see as they appear as little more than a change in the air. They’re not even as vivid as dreams, but the woman existed with them in their realm and she remembers them as impish creatures who always used to argue with the Guardians.

If you imagine the whole of existence as a straight line, the Guardians would sit at opposite ends, always in conflict, but usually evenly matched. Sometimes one of them will gain the advantage and then the Universe gets out of whack, but fortunately the Grace have a gadget that can put things back in order. The Key to Time is a perfect cube that holds time itself together - it can stop and start the Universe, re-write matter and change the states of quanta. In order to prevent anyone getting their hands on it, the Key is usually broken up into six segments and hidden throughout time and space, disguised as anything from statues to trees or even whole planets.

The unnamed woman and her sister were created to find the pieces so that the Grace could re-assemble the Key and put things back in order. There are two of them because it would be too much of a temptation to have one person collect them all, so they each have to find three segments. She remembers the explosion of information that entered her head when she was first created, but unfortunately the guidance she was given came from beings who’d never taken a single step into this Universe. She remembers the Grace being terrified of the Universe coming apart around them, but neither she nor Amy had ever learned to be afraid.

Ace leads the woman down a corridor in search of an escape route. There don’t seem to be any guards on duty, but there are automated systems all over the place. They need to reach the outer gate mechanism before the alarm is raised - but it’s too late and a loud klaxon sounds all around them.

It was raining when she arrived and the woman’s first taste of air was a bit of a disappointment. Suddenly, a man leapt out and grabbed her - then he pressed a button on his bracelet and they both vanished out of time. When they reappeared, they were surrounded by buildings and there were people were bustling all around them. The woman came from a place with no sound or colour so she found the noise here deafening. The man, who introduced himself as Harmonius 14 Zinc, said they weren’t far from the gateway where he’d grabbed her, but it wasn’t raining here as the sky was covered over. Her nose tingled and when she sneezed for the first time, she ended up laying on her back, looking up at the sky. Zinc helped her up and told her they were underneath a huge canopy which kept the atmosphere in. She told him she’d only been alive for three minutes and explained about the Key to Time, begging him to help her find the missing segments. She didn’t realise back then that in order to survive you have to keep secret anything that makes you vulnerable. Zinc taught her to know better.

Ace and the woman are soon returned to their cell. They realise they won’t get a trial now, but it doesn’t really matter as they were going to be found guilty anyway. Ace explains that she has a friend who can help them, but then she’s forced to admit that he doesn’t actually know she’s here.

The woman discovered Zinc had brought her here using a teleport bracelet that could take them any place and any time, but as he’d somehow been diverted, neither of them knew where they were. They wandered around, but the woman found the sights, sounds and smells overwhelming. Unfortunately his scanning equipment wouldn’t penetrate the dome above them so he couldn’t establish their position. The woman was intrigued by all the people going about their daily business, but she’d never seen people before, so it was Zinc noticed out how odd it was that everyone was smiling and wearing bright colours. Even though he and the woman were strangers, the people seemed to trust them and didn’t ask any questions. The woman had her first experience of eating food and she didn’t find it comfortable. The people refused any payment for the food and Zinc thought they were asking to be taken advantage of. Everyone here had been allocated their own assignment, such as painting the buildings or checking the seals around the windows, but the tasks seemed to be pointless and never-ending. The woman realised the people’s smiles were fake and that they were dead behind the eyes…

Zinc and the woman visited the town’s museum which included holograms of when the colony was first settled. In those days, the people didn’t smile and they appeared scarred and weary. They found a giant telescope on the top floor and the woman was drawn in by Zinc’s excitement, laughing as he let her try out the controls. She didn’t realise at the time that, like the people here, she was leaving herself wide open to being take advantage of.

Ace asks the woman to trust her and go along with everything she says. The robot constable informs them that they’ve forfeited their right to a trial, but Ace turns things around and challenges the officer to work out how they escaped. She points out that they don’t know who she is, how she got here, or how she escaped from the cell, and if they wipe her memory they‘ll never find out. The constable orders Ace’s fellow prisoner to reveal the answers - and to Ace’s surprise, the woman agrees to tell them everything she knows.

Zinc took readings from the telescope, then he and the woman sat together watching the stars while they waited for the results. Zinc was about to tell the woman about his wife when his bracelet revealed they were on a moon called Erratoon which was completely encased in a geodesic sphere. There was no way in and no way out and the people here had been trapped for generations. It used to be a prison planet and it must have been forgotten in the galactic recession. The prisoners themselves were long dead, but their descendants were now carrying out the same menial tasks that once kept their forebears busy. There were still robot constables here to keep the peace and if anyone stepped out of line, they’d be arrested and their memories wiped clean. Even though the woman had only been alive one day, she’d already learned so much that the thought of losing all that terrified her. She told Zinc they could use his bracelet to trace the missing segments of the Key to Time - not just the three she’d been sent to collect, but all six of them. Zinc laughed at her, then he operated his bracelet and disappeared, leaving her behind.

It was an hour before she’d finally accepted that Zinc wasn’t coming back. When the museum closed for the night she’d found herself alone with people for whom she had nothing but contempt. She realised it was she who’d caused the bracelet to divert from its course and bring them both here and that the tingling feeling she’d felt earlier was an indication that she was near one of the segments. She followed the sensation and found herself on the edge of a great lake, stretching off into the horizon. There were many people on the beach and sailing aboard boats, yet they all had the same dead eyes that she’d seen back at the town. But it was the water itself that attracted her interest. By now she was aware that other people found her appearance attractive, so she decided to use that to her advantage and she persuaded the owner of a boat to row her out to the middle of the lake. She had no regrets about killing everyone here as she regarded them as dead people anyway.

It was while she was on the lake that she saw the strange man with the straw hat and the funny umbrella. He was staring at her from the beach as if he knew who she was and what she was about to do. She was tempted to go over to him, but the tickling sensation she felt was so intense she decided to go ahead with her plan. She lowered her hand to the lake and gently brushed the surface of the water. In an instant, the entire area was filled with a blinding light - and then the lake completely disappeared.

The woman tells the robot constable that Ace had forced her to go with her and she explains how she was able to open the cell door. Ace is furious and knows the woman has condemned them both. The woman is convinced she will be spared the memory wipe, but the constable directs them both to the trial room where their sentence will be carried out. The woman tries to persuade the robot to take only Ace and insists that she didn’t steal the lake…

Where there had once been a great body of water, now there was just a deep crater. Everyone who‘d been on the surface, including the man whose boat the woman was on, plummeted down and died instantly as they smashed into the hard rock of the bottom. The woman laid there, surrounded by shattered bodies, listening to the horrified screams all around her, with the crystal segment in her hand. She got to her feet, ignoring the people from the beach who came rushing forward to find their friends and family. The man in the hat was attending a small boy who’d miraculously survived, but the woman felt nothing for them. She placed the segment in her satchel and then walked to the shore where the robot constables were waiting for her, having seen everything from their surveillance tapes. They didn’t understand what she’d done or how she’d done it, they just knew that she’d broken the rules and had to be punished.

As the process begins, Ace finds that she can still remember certain things. She can remember visiting the Trib Museum and she can remember the time she spent with the Doctor, battling gods and monsters. She can’t quite remember the name of the woman who travelled with them, except that she wore earrings and knew a lot about dead things. She remembers that a Time Ring had been stolen from the Museum and they’d come here on the trail of the thieves - Harmonius 14 Zinc and his wife 1V Magda, two small-time crooks from the Commune of the White Sun, a place known mainly for its tree-houses and a milk-shake called barp. Now they have a Time Ring, Zinc and his wife have been committing minor crimes all through time before returning to safe havens that they’d set up for themselves where one day they can retire and live off their trust funds.

Ace and her companions have been close on their heels and have witnessed occasions where Zinc and Magda have actually saved people and put things right. The Doctor was beginning to think that perhaps the criminals might actually turn out to be alright and that they could be left alone, but then they started to abuse their time-travelling abilities by looking into long unsolved mysteries and untangling conspiracies. When they began investigating the Disciples of Chaos, the Doctor announced that it wasn’t the right time for them to sort out that particular mystery.

That’s how Ace got stuck on the planet of rain. The plan was for her to ingratiate herself into Zinc and Madga’s company and stop them finding out what was going on here. People from all across the cosmos had been coming here to join what appeared to be a freaky cult and although Ace was curious to find out more herself, she trusted the Doctor and knew better than to ask questions. So she pretended that she’d survived a shipwreck and allowed Zinc and Magda to find her in the wreckage. She told them their pilot had decided to join the Disciples of Chaos and that he’d brought the crew here against their wishes. Her story appealed to the heroic ambitions of the time travellers and they allowed her to join them.

Ace found Zinc to be attractive in a scruffy unshaven sort of way and Magda was strikingly beautiful, as though her features had been sculptured from glass, but she constantly criticised her husband and was overly patronising towards Ace. The three of them walked through the rain to a stone gateway that the Disciples worshipped, but their original plan to grab a disciple and question him proved impossible as there was no cover nearby from which they could ambush anyone. Zinc had the idea of innocently approaching a disciple, grabbing them and using the Time Ring to teleport them to where Ace and Magda would be waiting. He set off on his mission, but never returned. There was no sign of him back at the gateway, so they assumed the Disciples must have captured him.

Ace and Magda set up a small camp inside a nearby wrecked spaceship and, for the first time, Ace felt she had the advantage over her companion as only she knew how to survive in these elements. They sheltered there for the night and Magda told Ace about the breeding programme of the Secondary Echelon and how she and Zinc had to run away because Zinc was from a lower strata. Despite her protests, it was obvious to Ace that Magda regretted leaving the comfort of her upbringing. They took turns keeping watch while the other slept, but when Ace woke up she found Zinc had returned.

Over breakfast, Zinc revealed that he’d grabbed a disciple and operated the Time Ring as planned, but that he’d got knocked off course and found himself on a place called Erratoon, a planetoid inside a geodesic sphere. While taking readings to find out where he was, he discovered it was packed with Elysium ore, a vital component in the fuel used to blast ships into hyperspace. It’d never been picked up by any previous survey because it was hidden by the geodesic shielding. In this time period, humanity was preparing to push out into deep space, so if Zinc and Magda made the first claim for mining rights on Erratoon, they’d be rich forever. Ace approved as she didn’t think what they were doing would harm anyone, so she decided to complete her mission and hope the Doctor could find her later.

Zinc and Magda took Ace with them to Erratoon, where he revealed that this used to be a prison planet. The penal service in the early years of the expansion had dumped thousands of people here and then sealed them in, writing whole generations off the books. The people here flourished and had families, but the robot wardens were still patrolling and supervising everyone, forcing them into generations of menial work. Ace couldn’t bear to think of all the blank-eyed smiling people living like slaves, but Zinc and Magda just saw them as willing saps. As they moved around and got a feel for the place, Ace noticed her companions were writing these people off just as the authorities had years ago. Zinc explained that galactic law insisted that first claims on mining resources always go to the native population, a policy designed to prevent wars or unfair practice, so he planned to smash the artificial sky, removing the native population - and the problem - at the same time.

Ace now saw Zinc and Magda for what they truly were. It was fine while they just wanted to scam people and make some money, but now they were plotting mass murder. She’d already convinced Magda she was an expert in pyrotechnics, so she volunteered to set up the necessary explosions, knowing she could deliberately make sure they didn’t work. She arranged to leave a trail behind that the robot constables could follow, but then she discovered they didn’t know anything about crime prevention and were only programmed to respond to crimes after they’ve been committed. She even tried to attract the attention of the people themselves by blatantly showing off the rocket she was building to destroy their sky, but everyone just nodded blankly and walked away. The only thing that seemed to interest the people here was the mystery of a missing lake which had completely disappeared earlier that day. Zinc was fascinated by the story too and both Ace and Magda realised there was something he wasn’t telling them…

Magda became impatient with Ace and as she’d run out of reasons to delay the launch, she had no choice but to fire off the rocket. However, she made sure the rocket exploded on the ground, even though it would mean she’d be arrested by the constables. She found herself being dragged into a cell, which is where she met her fellow prisoner, the young woman without a name, who explained that the punishment for those found guilty here is that they have all their memories wiped before being sent on their way…

Ace can’t remember anything after that. She can’t remember being strapped to the chair or the machine inside her brain that erased every thought she’d ever had. She can’t remember any of the events that made her the person she is. Suddenly an alarm goes off and the robot constables start defending themselves against an attack. The woman who’d shared Ace’s cell calls out in delight when she sees that their rescuer is Zinc, but after their successful escape back to their shelter, Ace is left alone in a corner eating porridge. The woman from the cell asks her how she’s feeling, but she doesn’t really know. She doesn’t even remember who the woman is, although she knows she was with her when they were rescued by the stranger. Ace has a vague recollection of another man who’d sent her on a mission, but she can‘t recall any of the details. The woman says Magda is jealous of her and won’t let her anywhere near Zinc, so she asks Ace to trust her and keep Magda busy for a while so she can talk to him alone.

While Ace is distracting Magda, the other woman takes Zinc back to the prison, stopping off on the way to pick up some heavy artillery. Zinc had heard about the disappearing lake and he now believed everything the woman had told him about the Key to Time and her hunt for the segments. Although she now knows Zinc is married, the woman persuades him that she would be a better offer. They both go to retrieve the satchel that was taken from her when she arrived at the prison…and before they leave Erratoon for good, they leave the constables details of where Ace and Magda can be found.

Ace still has some instincts of the person she used to be, so when she hears the robot constables approaching their shelter, she escapes through another exit. The robots seem content to arrest just Magda, so Ace runs off alone, even though she has no idea where she’s going. Not knowing that Zinc and the other woman have betrayed her, she hopes to get them to help her rescue Magda, but she can’t find them anywhere. Instead, she meets a strange man in a white suit and straw hat, who lets her hide with him until Magda is released a few hours later. Ace waits for an opportunity to approach Magda and ask her how she’s feeling, but Magda has a lifeless smile and there’s no recognition of Ace in her dead eyes.

Zinc tells the woman it was better for Magda to lose her memories than suffer from the knowledge that he’d left her. The woman can’t understand that as Zinc has taught her to be both selfish and wary, to take what she wants and then leave. It wouldn’t even bother her at all if Magda had been hurt.

Ace shares a meal with Magda, but doesn’t know what to say to her as she feels they’ve both been left behind and abandoned by the people they trusted. In her distant empty memories there’s a vague shadow of a man she once knew, but whenever she tries to think of him, his image is replaced by that of the man in the suit and hat. Magda has not only had her memory wiped, she’s also been given assignments by the constables, so after their meal, she leaves Ace and goes to check the windows at the habitation blocks. Alone, Ace concludes that she doesn’t belong here. Suddenly she hears the roar of engines and sees a rocket across the street launch into the sky. People gaze up at it for a moment, then they return to their chores, but Ace knows it’s important somehow. She rushes over, just in time to see the woman from the cell operate a bracelet and disappear. Ace watches the rocket get higher and higher and tries to work out what it all means…but then it hits the geodesic shield surrounding them and there’s a tremendous explosion. People start screaming, but there’s nothing anyone can do.

The woman had taken the Time Ring from Zinc while he was sleeping and returned before he woke up, so he never needs to know what she’s done. She’s learnt a lot from him already and she’s even had time to prepare a story in case he does find out. She knows they can’t gather up all six segments without someone catching on. She’s not bothered about Amy, but there’s the Grace and maybe even the Guardians to worry about. The last people to collect together the Key to Time ended up on the run with nothing to show for their troubles, and she’s determined that isn’t going to happen to her and Zinc. She’s made sure they have a safe haven where they can escape and now that the shielding around Erratoon has been destroyed, they can come back later and claim the first stake in the mining rights. She’s particularly glad to get Magda out of the way because she learned something from her too - how to be jealous. She and Zinc are now in this together, and there’s no room for anyone else. She’s already capable of being selfish, but she wonders what else there is for her to learn. For a moment, she considers making Zinc angry, but instead she tells him to set the Time Ring to take them to find the next segment.

Eventually Ace stops falling. Now, she can feel the dried blood in her nostrils and sense the medicine that’s helping to numb the awful pain. The man in the white suit and straw hat is with her. He tells her he’s a doctor, but he has the saddest eyes with more memories behind them than Ace can fathom. He helps her to understand that the buildings had been waiting for the day when Erratoon broke apart. When it happened, the buildings lifted off from the surface and sailed quietly after the people who were tumbling into the dark. Not a single person died and it only worked because for generations, all the emergency systems had been kept ready by the people who‘d been checking the equipment as part of their everyday mundane tasks. Ace has the strangest feeling that someone knew what was going to happen and was watching over them. The Doctor just smiles and she knows she can trust him.