Severus returned to the Mook Rehabilitation Centre several times over the next couple of days. Nobody – whether they knew he was a human wizard or not – seemed to object to a stray cat sniffing around, though he stayed alert in case any of the creatures in there wanted to eat him. He eavesdropped on a few one-to-one counselling sessions – even from the other side of a closed door, a cat's hearing is very sharp. Then he found himself listening to a session where a mook explained that he had been a would-be assassin whose target had captured and tortured him until he fell in love with his captor and…

Severus fled. What the man had been through had almost certainly been similar to Mark Vorkosigan's experience. Except that Mark had given permission for his memories to be viewed by strangers on the Rock (or by his brother's late bodyguard, for that matter) when he had destroyed the videos of them to prevent his own brother and parents from seeing what had happened to him. The nameless man in the counselling session hadn't consented to anything.

Severus had always been curious about other people's secrets, before he worked as a spy for either the Dark Lord or Dumbledore, even before he went to Hogwarts and became suspicious that the thin, sickly-looking Gryffindor boy was a werewolf. When he and Lily were children, they had enjoyed sneaking into Petunia's room to read her diary. After all, nobody told children the things they needed to know, so how else could they learn?

But now the thought struck him, This is what I was furious with Harry Potter for doing to me. Had there really been that much difference between him and Potter, at least as children? But now he was a grown man – chronologically, even if he was in an adolescent cat's body for the time being – and he ought to have more self-control.

Still, if he kept away from the private offices (maybe he ought to come back later, in human form, and offer to cast proper silencing charms to protect privacy?), the classes looked interesting. Most of them had small groups of no more than a dozen students, other than team sports that needed eleven or so on each side. Apart from classes to practise skills – painting, music, foreign languages, practical classes like cookery for people who had always lived in barracks and weren't used to planning and cooking their own meals – and relaxation techniques like yoga, many of the classes were about developing creative thinking skills, through improvisational drama, tabletop role-playing games, creative writing or storytelling. If he did ask to attend these, would he be turned down for being overqualified and taking over the group? It would be hard not to have a more domineering personality, not to mention more intelligence, than the mooks. But learning to play a musical instrument sounded very appealing.

In the evenings, he joined the Reformed Villain Support Group to watch the last few memories of the adventures of Miles and Mark on Jackson's Whole. His housemates had grown away from him, as they grew closer to each other. In the past, Severus would have been the one trying to reassure Konstantine when the images in the memories were triggering for him. But Severus wasn't good at understanding other people's emotions, and Konstantine wasn't good at even being aware of his own emotions, let alone expressing them, so it was Anakin who could directly sense when he was troubled.

And it was also Anakin who was the only one who could establish a direct psychic link to Severus and talk to him in dreams while he was in cat-mode. But Severus had been refusing to let him in. So, if they were going to communicate without using Legilimency, he needed to turn human again and actually talk.

When Anakin said, 'So, this was a slave who found freedom and really did return to his home planet to free the slaves,' and Cheiron said, 'Well, some slaves, anyway. Completely ending slavery on a planet is more complicated than you or Mark realised when you were younger,' Severus wouldn't have minded joining in the conversation. But it wasn't enough to be worth turning human for.

The moment that struck him, though, was Mark's line at the end of the third-to-last phial of memory: 'For the first time in my life, I am going home.' Home wasn't Jackson's Whole, where he happened to have been born, and home hadn't been Barrayar when he had been forcibly brought there to explain himself to the Barrayaran authorities. But it was home now: the place where his parents and cousins were, and where Kareen Koudelka was, who didn't have a familial duty to him but wanted to be friends with him because she actually liked him, and she might or might not still be willing to be friends with him once she realised how mentally unstable he was.

Home for Severus hadn't been Spinner's End or Hogwarts, the only two places he had lived in his mortal life except for three years between leaving school and returning to work there. Was this house, the place that he shared with Konstantine and Anakin, home? Possibly. He remembered his dream about decorating his bedroom to make it individual instead of just a shelter for sleeping in. Would the Mook Rehabilitation Centre become home, if he asked to move in there instead? Maybe not, but he could certainly spend more of his time there. Did Jennie even have a home? Maybe there was an empty building somewhere that she was in the habit of sleeping in. If so, she hadn't offered to share it with him.

He would try being human one more time, he decided, as he went up to his room. If he didn't like it, he would know it hadn't worked out, and could decide to be a cat for the rest of his time on the Rock.

He fell asleep curled up on the blanket, and woke in the middle of the night to find the breeze from the window chilly on his furless body. He pulled the cover over him, but, still feeling exposed, got up to shut the window. Where was his nightshirt? In the wardrobe, where someone – Konstantine, or one of the robots – had washed it and put it away since he was last human and had need of it. He pulled it on. It was longer than he remembered, coming down over his feet. Or maybe it was just because he was trying to do all this in the dark, without a cat's night-vision and without putting a light on.

He reached for the pearwood wand, lying on the bedside table. It was covered in rough, ridged bark, and felt more like a twig than the splinter that had broken off a pearwood box. But, as anyone who had met the Luggage knew, sapient pearwood's bark was emphatically not worse than its bite.

Rincewind's Luggage was, without a doubt, the weirdest pet belonging to any wizard Severus knew – and it was far more a pet, like Dumbledore's phoenix or Hagrid's dog or Filch's cat, than a mere magical artefact like most wands, broomsticks and similar. Or was it better to think of it as a person, a loyal follower or servant, like the bond that had grown up between Harry Potter and the house-elf he had tricked Lucius Malfoy into freeing? The Luggage, fiercely loyal to and protective of its master but able to transfer its loyalty from its original master to master's friend if its first master told it to do so, and a ferocious killer which was happy to do domestic tasks like sorting laundry, reminded him of what Konstantine might be like if he were ever reincarnated as a wooden box. Though it was hard to imagine Konstantine pestering strangers in a pub to feed him crisps and beer, or befriending drag queens and playing around with high heels and nail varnish, as Rincewind said the Luggage sometimes did.

The Luggage was a dog-like box, as Konstantine was a somewhat dog-like human. But the pearwood wand was Son-of-Luggage, and so, inevitably, it had the personality of a puppy. When Severus picked it up, it wriggled excitedly at being petted, and wagged its tip.

'Lumos,' Severus commanded it, and it emitted a beam of light. 'Good stick,' he told it, and it wagged its tip again, pleased, and urging him to play. 'Not now – it's the middle of the night.' The stick wriggled. 'Oh, if you insist.'

He opened the window again, and threw the wand away, as hard as he could, so that it could fetch itself. It somersaulted in the air and flew back to him, as it always did. But this time, before settling back into his hand, it rapped him painfully across the knuckles. Its meaning was clear: Don't you dare neglect me for so long again!

'Ow! Bad stick! If you don't behave yourself, we always need kindling for the stove,' grumbled Severus, rubbing his hand.

The stick wriggled, aware of his annoyance but also that he wasn't truly hostile. Throw me again!

'Oh, just once more, then.' He threw it, and this time it sailed back to him and settled contentedly into his hand without argument. It had just wanted some acknowledgement.

Severus was aware that something still felt wrong. Had he actually woken up in his own human body? He didn't have a mirror in his room, but from the glow from his wand, he could see that his hands looked younger and more childlike than he remembered. He pulled up the overlong left sleeve of his nightshirt. No Dark Mark.

Oh, God. He hadn't turned into Harry Potter, had he? He felt his face. No scar that he could discern. Same protruberant nose that he was used to, though his skin was spottier than it had been in years. Long, lank, greasy hair instead of Potter's wildly untidy thatch.

By wandlight, he made his way to the bathroom, switched on the big electric light overhead and examined himself in the mirror there. It was Severus Snape, no doubt about that. But it was Severus Snape aged about thirteen.

He hadn't been transplanted into some clone's body, had he? Some defenceless child, murdered to extend his own miserable life… He checked his face more carefully for scars in the mirror. No evidence of stitches around the top of his head. He lifted up the nightshirt and turned around, craning his neck to inspect his back. Yes, the scars his father had given him from numerous beatings were still there. A cloned body would be grown to be physically unblemished, unless, like Mark, they were deliberately created to be an impostor and systematically mutilated to match the original. So, not a clone then. Just de-aged.

Did he still have an adult's magical ability? Lumos was a simple spell which he had already been well used to doing when he really was thirteen. But would he be able to cast a more difficult spell – one that it had taken more effort to master?

He returned to his bedroom, grasped the wand firmly, and tried to focus on one of his favourite memories. Not one that he had shared with Potter. The first time that Lily and he, as first-years, had sneaked out of their respective dormitories to break into the Potions lab (his dormitory was in the dungeons close to the Potions lab anyway, but he had crept up to the Gryffindor tower to meet Lily and escort her down) to experiment with some of his ideas for improved versions of potions. That had been a good, and very giggly, night. He had been certain then that they would be best friends forever.

'Expecto patronum!' he called. Memories of Lily always brought his guardian in the shape of a beautiful silver doe, ready to drive away Dementors. 'Expecto patronum!'

Nothing happened. No Patronus, and no feelings of happiness, either. Thinking of Lily now just reminded him that they hadn't stayed friends. Knowing now that it hadn't been all his fault didn't make it any better.

He tried to remember any happy memories. At infants' school when he was four, listening to the teacher reading a story about a cat by himself in a tree? Or when he was six and the teacher had walked the entire class down the street to register at the local public library, and he had borrowed Comet in Moominland? He tried again: 'Expecto patronum!' There was a wisp of something silvery, but he couldn't clearly make out what it was. Books had made him happy, but they had never been enough to blot out the memory that he would soon have to go home, where Dad shouted and Mum cried.

He tried for more recent memories. The Slytherin Quidditch team's dazzling success against Gryffindor in the spring of 1991, and how annoyed Minerva McGonagall had been about it? That had been a good moment. 'Expecto patronum!' Nothing. Thinking about Quidditch that year just brought him back to memories of the following year, when Minerva had decided that the answer to Gryffindor's lack of success was to add to the team a first-year who had had no flying training since he was one year old and was the target of assassination attempts – and looked so sickeningly like his father, especially in the way he flew, that Severus couldn't manage to be dispassionate about him.

He dropped the wand. He might as well go back to sleep. He should never have tried being human. He had been far better off as a cat. He remembered a night a couple of months ago, sleeping curled up on Konstantine's bed, hearing Anakin's snores just a few yards away, and knowing that he would soon be joining Anakin in another shared dream, of swimming or duelling practice or whatever they chose. No, don't think of Anakin, being friends with him can't work. Going out for walks at night and meeting Jennie? Best not to think of Jennie – she won't want you now she knows you've turned human again. The time Nutt had spoken to him when he'd first attended the Mook Rehabilitation Centre in cat form? Maybe there was hope there. That time he had gone into a dream about things he wanted to do when he went human, like painting his bedroom and planting a garden? That had been a good dream, even if the Mirror of Erised coming into it, with the reminder of all the things he couldn't have, like a long life, a wife and children and grandchildren, had marred it. But – being in that dream with Anakin, knowing that if they could neither of them have that sort of happiness, they could at least have friendship, had been good. Maybe they still could – especially if his life started moving forwards at last, like Anakin's, and he wasn't just sulking around at home.

He picked up the wand one more time. 'Expecto patronum!'

This time something distinct took shape – but not the doe. This was a much smaller creature. He waited for it to bound away as the deer always did, but instead it rubbed its head against his ankles, asking to be stroked, as if it didn't know that it was just an image made of vapour. Had he fallen in love with Jennie so much that it now copied her shape instead of that of Lily's patronus?

No. This didn't look like Jennie, with her short coat, small neat head and big ears. She was elegant, but this patronus was covered in masses of long fur and looked, well, adorable. Had he really looked like that in kitten-form? And why did this patronus not run away? Why was it behaving as if it liked him?

Was he starting to turn into someone who liked himself? Not in the self-obsessed way that Gilderoy Lockhart filled his room with pictures of himself, but just – as someone who could accept himself, the way Nutt seemed to accept him?

If he stayed human – if he didn't renounce being human for good – he couldn't be Jennie's friend. But he was human. That was as much a fact as that he was a wizard. A wizard whose soul was catlike, in the way that Konstantine's soul was doglike and Anakin's was dragonlike, but still a human wizard.

Tomorrow night he would turn into a cat for the last time, to find Jennie and say goodbye. But for now, he needed to sleep, and then have a day of being human, to get used to it again.