Severus made himself a mug of tea and sat at the kitchen table. The fire in the brewing area he used for large batches of potion – separate from the small cooker they used for meals and drinks, and for one-off potions – had gone out, and the cauldron of calming potion looked all right for a first stage.

He was on his own. He could stop Occluding now. Give himself time to think the thoughts he had needed to avoid around Vader. Like why he had agreed to this insane plan in the first place. It went back to 1983…

After two years of teaching at Hogwarts, he had gone home for the summer for the first time. His parents were dead, and he had saved up enough of his wages to be able to go back to Cokeworth, have a bathroom built onto their old house to make it saleable, and then sell it and cut off all ties with his muggle past. The fact that the bathroom was an extension behind the kitchen rather than upstairs would be a blatant admission that this was not the sort of house which had originally had a bathroom, but it was trying to move up in the world. Like him.

At least in Cokeworth, he didn't have to worry so much about being recognised, or at least not as a renegade Death Eater. Few people in the wizarding world had even known that he was a half-blood and almost none of them – except Lily, who was now dead – knew where he came from, so he was fairly sure that his parents' deaths really were from the mundane causes listed on their death certificates, and not the result of leftover Death Eaters hunting down the blood traitor and her muggle husband who had spawned the coward who had done a deal with Albus Dumbledore instead of boldly standing up for his Death Eater convictions and going to Azkaban for them.

In Cokeworth, if anyone whispered about him, then instead of 'Evil bastard, they should've locked him up and thrown the way the key, if he wasn't Dumbledore's pet, the Dementors' Kiss is too good for him…' it was only, 'Tobias Snape's lad, haven't seen hide nor hair of him since he got a scholarship to that posh boarding school, same one the Evanses' younger girl went to, who knows what became of her, these boarding schools, even worse than ordinary grammar schools for making kids forget where they came from and think they're too good to mix with the likes of us…' which wasn't comfortable either.

On one occasion he had shouted, 'If you must know, Lily and her husband were murdered! In front of their baby! Because they were fighting terrorism! And Lily was too good for this filthy town!' Shouting this in a pub full of unfriendly men hadn't been a good idea, but it had shocked everyone into silence for long enough for him to slip away without needing to use magic to defend himself.

After a couple of days, he had been so desperate to escape from reminders of everything in his life, the magical and muggle side of it alike, that he had gone to watch some nonsensical film involving spaceships, sword-fighting, and aliens who looked like teddy bears or giant slugs – or, admittedly, house-elves painted green. The hero was a young wizard about Severus's age, trying to learn to be a wizard in a world in which there were barely any qualified wizards left to train him, apart from an elderly elf who soon died of old age, and the Dark wizards whom he had to defeat – one of whom was his father. Severus could sympathise with him there. His own father had been bad enough, but at least he had never gone so far as to chop Severus's hand off.

He hadn't meant to get so caught up in the story instead of loftily disdaining it as nonsense made by muggles who had no idea how magic really worked. He certainly hadn't intended, by the end of it, to be sobbing his heart out at Darth Vader's death. He couldn't understand why he was reacting so strongly. He hadn't known how to react to his own parents' deaths – he hadn't seen either of them in years, and they hadn't even seemed real compared to his fears for Lily. And when Lily was murdered even though Dumbledore had promised to protect her, he had felt like a hypocrite for grieving when it was his own fault she'd been killed. But here, in a darkened cinema, it was safe to cry for the bad choices he had made, and for the fact that he would never be able to confront his father as one adult to another instead of as a terrified child, and perhaps come to understand him enough to know whether there was any good in him. (There probably wasn't, anyway.)

And then the film had finished, and he had dried his eyes and gone home to experience the novelty of being able to have a bath without being ogled by a teenage ghost who had never forgiven him for guessing her nickname (well, considering that she had apparently spent much of her time skulking in the toilets even when she was alive, and that her name was Myrtle, and that a lot of the potions used the common marsh herb myrica gale, what did she expect? – though he still deeply regretted having used the name to her face, when he was sixteen and miserable after quarrelling with Lily, and had alienated both his living friend and his ghost friend on the same day), and also for having become a follower of the boy who had murdered her. The summer had wound on, and he had gone back to Hogwarts to prepare for the start of the autumn term. Nobody at Hogwarts needed to know that he knew who Darth Vader and Luke Skywalker were. For a while, some of the muggleborn students had nicknamed him 'Darth Snaper', but this had soon been overtaken by the much juicier student rumour that he was a vampire.

When he had died and arrived on the Rock, he hadn't had any particular plans for the afterlife, other than that he might combine potions research with brewing whatever potions the people of the Rock needed, and that he never wanted to work in a school ever again, whether between lives or in any future incarnation. Being a mentor for reformed villains hadn't even occurred to him. Or it hadn't until he had met Konstantine, at any rate.

Anyway, back to the present day. He ought to start preparing ingredients for the second stage of the calming potion, while Vader was asleep. After all, he, Vader and Konstantine were all likely to need it frequently. Then he ought to start working on a batch of Dreamless Sleep – Cheiron discouraged patients from using it regularly, but it was worth having some in reserve.

He had just assembled ingredients for the calming potion when there was a knock on the door. Sighing, Severus went to open it. Of course Cheiron would want to know how they were getting on.

Like most of the houses on the Rock, this one had the ground-floor ceiling high enough and the door tall enough that a centaur could walk in. Cheiron was small for a centaur, only about the size of a pony, but good-looking, with his chestnut coat and golden tail matching his blond hair and auburn beard, and with the feathery white fur around his four hooves. In his lifetime, Severus had sometimes seen paintings of Cheiron which showed him with a man's legs and genitals in front and the back half of a horse sticking out from his rear end, which had always looked peculiar. He had been relieved to find that the real Cheiron just looked like a normal centaur who wouldn't have been out of place in the Forbidden Forest herd.

'Good afternoon,' Cheiron said. 'How's it going?'

'Badly.'

Cheiron sighed. 'Severus, I'll say it again: if you're not comfortable with this, you don't have to go through with it. I know Konstantine was looking forward to adopting Anakin, but it won't work unless you're both right behind the idea.'

'Konstantine is the one who is fighting with him!' Severus retorted. 'Vader had to use magic to defend himself after Konstantine flew into a murderous rage because Vader was reading his mind!'

Cheiron nodded, waiting to hear more. It was infuriating. Instead of saying something reasonable and placatory that implied that Severus might be exaggerating, he waited for Severus to do this himself.

'In fairness,' Severus went on through gritted teeth, 'they are both trying to control themselves. Vader didn't use Dark magic or anything that causes injury, only something like a shield charm, as far as I could see. And Konstantine was planning to go and talk to you anyway, once he'd taken some time to calm down.'

'That's a start, then,' said Cheiron. 'What about you? How do you feel about Anakin?'

'He's a pallid-white, disfigured revenant who survived injuries that should have killed him, through means that almost certainly included Dark magic, he's a mass-murderer who has repeatedly massacred children, and he's known as the Dark Lord. How do you think I'm likely to feel about him?'

'I can guess at how you might feel,' said Cheiron. 'But I'm asking how you actually do feel, meeting him face to face?'

'He's – not too much trouble, if I keep Occluding,' Severus admitted. 'After a while, we even managed to have a civil conversation. Mainly, it's peculiar seeing him without his armour, because that makes him look less like Darth Vader in the film, and so that makes him look more like the Dark – my world's Dark Lord.'

'Do you think you'd be able to think of him as Anakin? Or at least as Skywalker, if you don't feel ready to be on first-name terms with him?'

Severus tried the names out in his head. 'No.'

'Do you realise that "Darth Vader" wasn't even a nickname he gave himself?' asked Cheiron. 'It wasn't like you as a teenager deciding to call yourself "the Half-Blood Prince" or Tom Riddle deciding to change his name to "Lord Voldemort". It was a slave-name that Emperor Palpatine gave him to taunt him, because it means "father" and, as far as he knew, he could never be a father because he had murdered his pregnant wife. How would you feel if everyone insisted on calling you by the name James Potter used to call you by?'

'That's not the same! Anyway, why does he need time to convalesce?' Severus hastily changed the subject. 'When I cast spells to heal his wounds, they barely did anything. Why didn't they work?' He didn't have the training to regrow severed body parts (he winced, remembering the time he had accidentally cursed off George Weasley's ear), but he was good at dealing with lacerations (he winced again, remembering finding Draco badly wounded because Harry Potter had been stupid enough to try out some spell he had found lying around without having any idea what it did – well, okay, because he, Severus, had been stupid enough to leave his old textbook with spell notes scribbled in the margins lying around).

'Perhaps it's because he's recovering well without needing magic,' said Cheiron. 'You know how healing magic has different rules in different worlds, don't you? In your world, any competent healer can mend a broken limb instantly by waving a wand, and having all the bones from someone's arm conjured away is considered a severe injury because it takes a whole night to regrow them! But in other worlds, it would be more a matter of using magic to set the broken bone and ward off infection, but you'd still need to immobilise the limb and give it time to heal naturally. Sometimes there are limiting factors – for example, a sorcerer whose powers come from a chaos demon can only work healing magic for a while before needing to shed some chaos by killing vermin – and in some worlds, if you use magic to heal a muggle, there's a risk of accidentally enchanting the muggle so that they will fixate on you, and even re-injure themself in order to be healed again.

'Now this place is between the worlds, and it doesn't necessarily obey the rules of whatever worlds people came from, but it does seem to have its own rules, though I don't fully understand them myself. I think if Anakin had really needed magical healing, you'd have been able to heal him, but as it is, with the bacta tank that somehow arrived here from his own world, and Rowan's skill as a surgeon, he's recovering well. Maybe his mind wouldn't even be able to adjust to the experience of suddenly being completely healthy and non-disabled, after so long. Maybe the experience of being well cared for and having time to rest and heal, and learning that he can trust the people around him and that it's safe to be unarmoured and vulnerable, is what he needs most, right now.'

'At the moment, he's mostly treating it as an opportunity to practise levitation charms,' said Severus.

'That's no bad thing, either,' said Cheiron with a smile.

Author's note: I have mostly tried to stick to canonical descriptions of characters. However, I find the ancient Greek paintings of Cheiron that depict him with human genitals and feet – sometimes slash art showing him as Achilles' lover, which is shocking by modern standards considering that he was Achilles' teacher – as weird as Severus does, so I arbitrarily decided that Cheiron in my stories doesn't look like that.