Remus had gone to the cinema a lot in the years following James and Lily's deaths. It was easy enough for a wizard to sneak past the ticket stand undetected, and, once in, he could sit somewhere warm and dry and not think.
So he knew his part, from hundreds of scenes among the thousands of films he'd seen, and he played it reflexively. He waved goodbye to Harry, Hermione, Ron, and Ginny; he murmured reassurances to Molly, who was anxious at having her two youngest leaving her for another year, especially in these times. When the train began to move, he even followed it for a few steps, coming to a halt long before the end of the platform and raising his hand in a last farewell.
He barely glanced at the large black dog, which at first gamboled beside him, before it subsided with a self-pitying sigh and a whimper. He ignored that, too.
At last, the train was out of sight, and he turned back to the small group clustered on the platform. Moody had stumped off already, but Remus knew better than to think that he'd thereby missed the lecture on keeping Sirius under control. Never mind that he hadn't even been there when Sirius had made the decision to leave Grimmauld Place.
"Well, we're off to work, then," Arthur said. "See you at dinner, Remus?"
"I'm not certain. Probably."
"In that case, we'll see you when we see you," Tonks put in. "Ministry, ho!" That rousing cry was followed by her tripping over her own robes as she turned around, and Arthur placed a steadying hand on her elbow.
"I shouldn't be late tonight, my dear," he said to Molly.
She tucked a damp handkerchief back into the pocket of her robes. "I've heard that before," she said with watery acerbity. "Oh, well. Dinner will keep either way."
Remus waited until Arthur and Tonks had Disapparated. Then he drew his wand out of his robes and conjured a leash, one end grasped in his hand and the other wrapped around Padfoot's ruff. Padfoot gave a sharp bark, and Remus tugged on the leash. "Quiet, you," he said. "You know what the Muggles are like. It's a wonder nobody phoned the police or a dogcatcher on you this morning."
He met Molly's startled eyes. "Shall we?"
She pressed her lips together--Remus rather thought she was concealing a smile--and nodded. Molly might tend towards excitability, but being the mother of seven had also left her unflappable in some of the best ways.
"What the fuck was that all about?" Sirius hissed as soon as they walked through the door of Grimmauld Place.
"Not in the front hall," Molly said, glancing significantly at the curtains covering Mrs. Black's portrait. "I'll just go put the kettle on."
"Well?" Sirius asked, ignoring her admonishment.
Remus finished unlooping the leash from his wrist and banished it. "Exactly what I said in the train station. It's illegal for dogs to be unleashed in London."
"Nobody cared, Remus."
"No one who saw you the first time you were out cared," Remus corrected. "That's no guarantee for the next time. Your luck can't hold forever, Sirius."
Sirius grimaced eloquently at him, and Remus shook his head. "I need some tea."
They barely had ten hours to be stiff and uncomfortable in each other's presence before Dumbledore sent Remus off on another mission, this time to Hungary. Naturally, he couldn't risk firecalling Grimmauld Place while he was gone, and the enforced week-long silence weighed more heavily on him than it would have if he and Sirius had simply been avoiding each other in the same house. Still, it gave him the time and opportunity to make certain preparations.
"I have something for you," Remus said, entering the library.
Sirius's hand shot to his wand even before he looked up. The wariness in his eyes was replaced by confusion when he saw that whatever Remus held in his closed hand couldn't possibly be either wand or noxious potion. "You got me a gift?" he asked, sounding faintly embarrassed. "You didn't have to do that, Moony. If anything, I should get you one. You were right about the whole King's Cross...outing. I should've been more careful."
Even knowing that Sirius meant more careful not to be seen by Malfoy rather than more careful not to go in the first place couldn't keep Remus from melting a little at the apology. All he said, though, was, "It's not a gift, exactly." He opened his fist to reveal a black leather collar, studded with metal bits. "Here. Put this on."
Sirius laughed. "Aren't you always complaining that I act too much like Padfoot even when I'm not being a dog? I hate to break it to you, but giving me a collar is hardly negative reinforcement."
"Why don't you let me worry about that?" Remus asked, holding the collar out to Sirius.
Sirius shook his head. "I don't think so, Moony. Thanks for the gift, and all, but can you imagine what people would think if they saw me wearing that? I'd never live it down."
"Collars are very...um, trendy among Muggle teenagers nowadays, and this one's rather more stylish than most." Remus lifted it to inhale the rich scent. "Real leather, too." He offered it to Sirius again.
"There's such a thing as fake leather?" Sirius asked, puzzled. "What do they make it out of, tree bark?"
"Um, plastic, I think. In any case, it wasn't a request. I didn't ask you, Sirius. I told you to wear it."
Sirius's eyes went wide. "Moony?"
He didn't seem disposed to argue further, but Remus wasn't about to take any chances. He dropped the collar into Sirius's lax hand. "Now, Sirius."
He watched with satisfaction as Sirius raised the collar with hesitant hands and buckled it around his neck.
An odd expression crossed Sirius's face. He traced the collar with one fingertip, then ran it along the underside. He shrank down into Padfoot, shook his head violently a few times, and transformed back.
"Moony," he said. "What did you do?"
"Sorry," Remus said, not very apologetically. "You weren't supposed to notice that."
"How could I not? I can't take this damned thing off. That's not exactly subtle."
"Is that all you were referring to?"
"Well, no," Sirius admitted. "What is it? It feels...sounds...I don't know, but it's this sort of whirr. And, considering it's now permanently strapped to my bloody neck, I'd like to know if it's...whirring...because it's supposed to do that or because you bollixed up the charm and my head's about to explode any moment."
"Your head's not going to explode," Remus assured him dryly.
"What's this...thing...doing, then?"
"It's a collar," Remus said. "You may as well get used to the idea--and the word--because, as you've already noted, it's not coming off."
"What, never? But people will see! And don't give me any more of that rubbish about it being popular; you know exactly how little attention Snape pays to Muggle fashion." Sirius moaned dramatically. "I can just imagine what he'll have to say about something like this."
"Then I suggest that you invest in a couple of high-necked robes. The collar's irremovable."
"Oh, no, it isn't. I'll ask Tonks to take it off for me next time I see her."
Remus shook his head. "She won't be able to. It's a highly specific charm. Only I can remove it."
"Moony!" The note of outraged reproach in Sirius's voice was even stronger than before. "Why would you do something like that?"
"For the same reason that you need the collar in the first place: you've been a bad dog." Remus gave the last two words a stern inflection.
Sirius cringed visibly. There was a brief silence. "Somehow, that joke's not very funny anymore," he said.
"I'm not sure if it ever was a joke, really. In any case, the charm you're sensing is a modified tracking spell. It's designed to alert me anytime you leave the house and to help me locate where you've gone."
"Why not cast a charm to not let me leave in the first place?" Sirius asked bitterly. "'S what you want, isn't it?"
Remus shook his head. "I don't want to trap you. Besides, what if the house caught on fire, or something--it's less likely now that the Weasley twins are back at Hogwarts, but not impossible. I won't lock you up here. I just want to know when you're in danger, is all."
"Much good that'll do you if you've gallivanted off to Bolivia on Dumbledore's orders."
"I'm not gone all that often," Remus said. "And even if I were out of the country when you decided to leave Grimmauld Place, I'd still want to know about it."
"What, just so you can chew your fingernails for however long your mission lasts and then come back to find that I'm perfectly fine--or perfectly dead--and nothing you could have done about it either way?" Sirius asked skeptically.
"Yes," Remus said.
Sirius looked taken aback by that simple answer. "Oh."
"Anyway, you must have had some notion of what the collar was for, even if only subconsciously. Why else would I ask you to wear one?"
Sirius snorted. "As I recall, there wasn't much 'asking' about it."
Remus shrugged that truth away. "Nevertheless."
"Well, actually... I thought...I thought it was some sort of deviant sexual...thing."
Remus willed himself not to blush. "I wouldn't do anything like that to you, Pads."
"No. No, of course you wouldn't."
Sirius's voice sounded a bit forced, and Remus looked at him in concern. "What is it?"
"It's only..." Sirius laughed shortly. "Well, I did put it on when I thought that that was it, didn't I?"
Remus looked at Sirius sharply, but Sirius was staring at the floor, refusing to meet his eyes. There was a long silence. Sirius couldn't possibly mean...could he? "Well," Remus said slowly, "there might have been a bit of that, too."
Sirius raised his eyes, a half-hopeful expression lightening his features.
"Sirius," Remus said, his voice firm and implacable. "I want you to go up to my room, take off your robes, lie down, and wait for me." He permitted himself a small smile, though his heart pounded a furious rhythm in his chest. "The collar, of course, will remain on."
He held his breath, almost expecting Sirius to burst out laughing at his order, and wondering how he could bear it if he did.