Snape was standing at the top of the Astronomy Tower, scowling at the sky.  

It was an unwholesome kind of day - the weather looked as though it was working itself up for a storm, but it hadn’t quite got there yet, and so the clouds had turned a queasy-looking yellow and were hanging low over the castle, wheezing with half-hearted thunder.   

The door to the Tower opened, and Regulus Black came over to join him, grinning in that cheerful, insolent way of his, as though they were best friends.

“Alright, Sev?”

“Don’t call me that,” Severus replied, without looking at him.

“Fair enough,” said Regulus affably. “My mum calls me Reggie, and I hate that. I used to know a girl who called me ‘Regulars’. Muggle-born. Couldn’t understand a word of Latin, always mis-pronouncing her incantations. I swelled her tongue up with an Engorgement Charm in the end. She nearly choked to death.”

Unwillingly, Snape looked up from his contemplation of the sickening sky. “What do you want?” he said.    

Regulus Black had mossy green eyes and pointed teeth. Other than that, he looked almost exactly like his brother - all heavy, brooding eyebrows and romantically-cascading dark hair. Girls still giggled and swooned when he walked past, but they were nervous giggles and terrified swoons. There was something unsettling about him.

Still, Regulus was sufficiently similar to his brother for Snape to clench his fists involuntarily at the sight of him.  

Regulus was used to it. Snape was always angry. In fact, he would have been more uncomfortable if Snape had looked happy - that generally meant that he was contemplating practising some new curse on you.

In any case, Regulus had an ability to be comfortable with almost anyone, simply because he was much too arrogant to entertain the notion that his company could ever be unpleasant.

“Did you get caught last night?” he asked cheerfully.

“Yes and no,” Snape replied.

“They’re saying the Dark Lord was in the grounds somewhere.”

“Are they?”

Snape was still seething about Potter. What had he been doing by Lily’s bedside in the Hospital Wing, under an invisibility cloak?

He’d always thought that cloak shouldn’t be allowed. Every way he looked at it, it was unjust: it was simply too easy to lurk in changing rooms and showers, watching girls. And a teenage boy who hadn’t thought of putting the invisibility cloak to this use didn’t deserve to own an invisibility cloak.

“But you didn’t see him?” Regulus prompted.

Snape snapped out of his reverie. “Listen, if you’re still going on about meeting the Dark Lord, you’re going to have to give me something a little bit more concrete than the fact that your uncle’s Minister for Magic.”

Regulus was twirling his wand absent-mindedly between his fingers. He had a tendency to do this.

“What would you say,” he began, with the air of one cradling a dramatic bombshell, “if I told you I could get the Minister for Magic under the Imperius Curse?”

Snape raised his eyebrows. “I’d probably say ‘You’re lying’. If I was feeling nice. And I must warn you, Regulus, I’m not.”

Regulus’ insolent smile flickered for a moment, but he hitched it back in place. “Can you at least arrange for me to meet Lucius Malfoy?”

“Talk to him yourself.” Snape replied.

“You’re not in a very good mood today, are you?” Regulus asked perceptively.

Snape gave him a withering stare, but Regulus was adept at not taking hints.     

“Why don’t you tell me about it?” he asked. “After all, a problem shared is a problem halved.”

“Regulus,” Snape said patiently, “you’re doing it again.”

Regulus had been hit over the head with a very powerful magical object in his second year (thrown, it was widely believed, by his brother, Sirius), and he’d never been quite right since.

The statue that had nearly split his head open all those years ago had guarded the entrance to Dumbledore’s office before the present gargoyles had been recruited. It was a bust of a bald man with a nobly-lined face, wearing a Laurel Wreath, who would shout out proverbs or advice in a shrill voice to anybody who passed by. He was called the Random Wisdom Generator.  

At first, everyone had thought that Regulus had escaped the attack with only a concussion and a few scratches but, as the days had gone by, they had realised that the collision had done him permanent damage. Somehow, he had absorbed the Wisdom Generator’s power. He was insuppressibly wise. And he had no control over it.  

It was a regular feature of classes to hear Regulus shout out:

“Don’t count your dragons before they’re hatched,” or, “No use crying over spilt potion.’

Snape had once passed him in the corridor, and distinctly heard him mutter: “Pleasure is misleading, but you know exactly where you stand with pain. Pain doesn’t lie to you, it doesn’t flatter you, it doesn’t let you forget that you’re just a man.”

Thinking that he should convey this sentiment to the compulsively sadistic Bellatrix, Snape had hurried on his way, unwilling to be drawn into a one-sided conversation, in which proverbs would be thrown at him like missiles.
Regulus blinked and shook himself. “Sorry,” he said.

“See, what are you going to do if you start talking like that around the Dark Lord?” Snape asked peevishly, but he stopped, because his thoughts had strayed, as usual, to his revenge on Potter, and an idea had just occurred to him.  

“You know you’re always sneaking around, setting traps for the Gryffindor Quidditch team?” he asked urgently. “How come Potter hasn’t caught you? He’s got that map that tells him where everyone is.”  

Regulus grinned. “Set up a meeting for me with Lucius Malfoy.”

Snape suppressed his impatience and managed a shrug. “All right,” he said. “Your funeral. Now, how do you fool the map?”

“Two ways. Number one, use somebody he’s not interested in, somebody that he won’t be watching, to do whatever it is you want done: i.e. not Severus Snape or Regulus Black - and I wouldn’t be that red-haired Gryffindor girl, either - he’s always watching her.” Regulus paused. “In fact, if you could get her into trouble - maybe lock her in a room with a troll or something - he’d probably go charging off to rescue her, and you could - ,”

“Yeah, what’s the second way?” Severus interrupted.

It took Regulus a little while to respond; he seemed to be still imagining the scene with Lily and the troll locked in a room together. He was easily distracted. Snape nudged him. “Oh,” he said, shaking himself again. “Number Two, just make yourself Unplottable. The Charm can be modified to work on people as well as places. Do that, and you won’t show up on the map, even though you’ll be visible to everyone else.”  

Snape blinked. It was laughably simple. Why hadn’t he thought of it?

They turned suddenly, as Professor Caladrius opened the door to the Astronomy Tower, saw the two of them on the battlements, shuddered, and then shut the door again.

A silence followed this bizarre scene, in which Regulus twirled his wand and Snape started thinking, again, about Potter’s lurking presence beside Lily’s bed.  

“You want to know something about that Caladrius?” Regulus whispered, when he was sure that the teacher was out of ear-shot.

“Not really.”

“I have him for Divination,” Regulus went on, again unable to fathom that his conversation could be anything but fascinating. “He was acting really weird around me in class - wincing whenever I came near, backing away, that kind of stuff, as though he was allergic to me or something. So I asked Slughorn what his problem was.” Regulus grinned proudly, “he’s a mine of information, that Slughorn - you have to butter him up a bit first, of course, but give him a box of crystallised pineapple and a few compliments and he’s putty in your hands. Apparently, Professor Caladrius only has visions about the way people are going to die. All he has to do is stand near them, and he sees their deaths.”

Snape froze for a second; he’d just remembered something Dumbledore had said last night before he’d noticed his two students in the corridor:  

“If he has indeed discovered the nature of your visions, then you are in terrible danger.”

“That’s why the Dark Lord was looking for Caladrius,” Severus murmured, forgetting for a moment that Regulus was there. “He’s obsessed with conquering death. Caladrius would be able to tell him whether or not he ever succeeds.”

Regulus was silent for a moment. Then he said:

“Severus! We could bring Caladrius to him.”

“What?”

“Well, think about it. Whenever I go near him, he’s essentially incapacitated. It wouldn’t be too hard to -,”

“Smuggle him out of Hogwarts, right under Dumbledore’s nose? Yes, it would. You underestimate him. Especially now he knows that the Dark Lord’s after Caladrius. He’ll be watching him like Mad-Eye Moody watching a bartender who’s fixing him a drink.”

Regulus was silent again. “We could think of something…” he muttered.

“I’ve got my own problems right now,” Severus replied decisively. “I haven’t got time to go kidnapping teachers.”

“What are your problems, deciding how best to kill James Potter?” Regulus asked impatiently. “You’re not looking at the big picture. You want to be somebody, don’t you? This is the way to do it.”  

“There are less suicidal ways,” Severus replied.

“They would also be less spectacular.”

Snape gave him a sneering smile. “You Quidditch players!” he exclaimed.  

He was quiet for a moment, looking out over the castle grounds. “Next month,” he said. “Ask me again next month, after the Gryffindor-Hufflepuff Quidditch match.”

“What’s going to be different next month?”

“Everything,” said Snape.