Disclaimer: I don't own it but I can keep deluding myself…

A/N: A friend and I were watching PoA the other night and we both wondered why it was that Lupin required no explanation from Sirius. This was born.

This could be a sequel to Overanalysis if you squint.

There it was again. This was the third night in a row. There he was again.

How no-one else had noticed was beyond Lupin. Perhaps it was just because he knew what or rather who, it was. He daren't ask any of the staff if they had seen it for fear that they learn of his lies. They would finally have a reason to distrust him and Severus Snape would have a field day.

Still, there was no mistaking him standing bold as brass in the middle of the grounds. Lupin daren't even think it for fear that it would lead to the point of no return regarding his paranoia, but was that dog looking at him through the window?

Regardless, he drew the curtains and tried not to think about it.

Just what the hell was he doing here? He appeared to be waiting for something. Lupin frowned and peered through the small gap in the curtains. He blinked furiously. The dog was now preening. He was so sure of himself that he could afford the time to smooth out his fur? This was ridiculous.

Right, well he'd have the shock of his life. Lupin knew he couldn't report the presence of a dog and demand that he be checked by a Ministry Official but it was worth a shot. Perhaps he could pull it off so long as he looked surprised when he was proven right. No use; he was a terrible liar.

Nevertheless, he reached for his wand and half crept along the corridor, wondering whether he ought to head back to his office for the map. He rolled his eyes. He knew the corridors of this castle without the aid of that bloody map; the symbol of their friendship and sacrifice.

He was so relieved to have reached the grounds without detection that for a moment, Lupin wondered what he was doing out there.

Darting around the corner, he came face to thighs with the dog. Why had he moved? What had he seen? Had he known Lupin was looking for him?

Lupin shook himself and pointed his wand between its eyes. "Change."

The dog stared up at him with an odd glint in its eyes.

"I'm telling you to do it before I do it for you."

The dog actually sat down before him and curled its tail around its legs. The arrogant arse had always been like this, he didn't know why he had expected anything less.

"Don't bluff it out, Black. I know it's you."

The dog bared its teeth in what Lupin recognised as a smile. He shuddered and tried to retain his composure as the dog gestured for him to follow.

"If you're harbouring the delusion that I'm going anywhere with you, you can think again."

The dog sat again and shot him the same look he had become accustomed to while they were at school; the stare out, the argument without words. It was a look that said 'Oh really?' and Lupin's usual response was to smirk and nod in response. His hands shook.

"Where?"

As the dog padded towards the forest, Lupin laughed mirthlessly. "If you think I'm going in there-"

The dog gave him no choice. He did not even turn to acknowledge his one-time best friend. Lupin snarled and clenched his fists, slamming them into his thighs and wincing. He threw a backward glance toward the castle. There was no light and very few signs of life. With a world-weary sigh, Lupin followed Black to the outskirts of the forest where the latter waited for him in human form.

Looking into his eyes, Lupin realised how exposed and unprepared for this moment he was. Deep down, as much as he hated Black, he did not want him to suffer at the hands of the Dementors and so seclusion was absolutely necessary. Whilst making Black writhe in pain had been high on his list of priorities, he knew he was incapable of doing so.

"Well, well, Professor," croaked Black. "We've got to stop meeting like this."

"Come on then," he hissed. "Take your shot."

Black frowned. "What are you harping on about?"

"Well, you've killed everybody else. I'll be honest, Black, I'm starting to feel a bit left out."

Black's eyes widened in shock. "Remus, you really do have the sickest sense of humour imaginable."

"I could say the same," snapped Lupin, gripping his wand. "And frankly, I've had quite enough small talk. Give me one good reason why I shouldn't tear you apart with my bare hands."

Black swallowed hard and paused for a moment, staring deep into Lupin's eyes as though reading his very soul. He shook his head. "No, Remus. You don't have it in you."

Lupin pushed his wand into Black's chest. "I wouldn't test me if I were you." His eyes blazed, large, charcoal fires. "I don't have a friend in the world and it's your fault. I have been through one-hundred and forty-four nights of hell and it's your fault. I have had to listen to your godson telling me about what he hears when the Dementors come near him and that is your fault."

Black shivered. "Remus, I-"

Lupin scoffed. "If this is more of your bullshit, I've had more than my fair share of it. I honestly don't want to hear it."

Black gave him a bitter half-smile. "If you didn't want to hear it, Remus, you wouldn't have followed me. You have absolutely no intention of telling anyone I'm here so you might as well admit it."

Lupin sighed. "Why do you always do this? I hate you. I hate you so much that the only person I hate more is myself. You don't understand. I'm starting to wonder if there's even a soul for the Dementors to take."

Black grabbed his arm and held a struggling Lupin. "Listen! I killed them, I don't deny it. I'm a coward and a killer, Remus, and for that reason I am going to kill Peter Pettigrew. That's why I'm here, Remus. I'm here for Peter."

Lupin pulled away with such force that when Black freed him from his grasp, he staggered backwards. His teeth were bared and he shook with anger and disgust.

"You murdered Peter years ago."

Black shook his head. "I won't deny it, I certainly gave it my best shot but I didn't kill him."

Lupin shook his head. "He's dead. I went to his funeral."

"What did they bury? The bloody finger he hacked off?"

"YES!"

Black was shaken by Lupin's scream. He took a step back and appeared to be on the brink of fleeing. He opted instead for attempting to calm the usually composed Lupin whose outbursts were rare.

"Remus, there was no body, remember? Peter removed his own finger. He transformed and buggered off into the sewers with the other rats. He took half the bloody street with him and I couldn't prove anything. The only person who could was you and I'd lied to you."

Lupin slowly shook his head. "You've gone mad."

Black nodded. "That's entirely possible, Remus, yes. I may be mad but I am not capable of such fantastic lies and I believe that you know this."

Lupin stared at him, incredulous and beyond words.

"You do, Remus," Black persisted. "You do or you wouldn't be here with me. You'd never have agreed to follow me."

Lupin smirked. "Make no mistake; I followed you because I know I can outrun you. I'm the better duellist and I can curse you into next year. That's why I agreed to follow you. It was not because I trust you. It was not because I miss you. It was certainly not because I always used to believe the lies you spun and thought I'd give it another shot for old times' sake."

Black's desperation was evident in his tone. "Remus, please."

Lupin nodded, seemingly understanding this unasked request. "If you come anywhere near Harry, I will personally drag you to the Dementors by your own hair."

"Remus-"

"Shut up." It was almost a polite request. It was quiet and unassuming. The only thing missing was 'please'. "I'd get out of here if I were you."

Black shook his head. "I'll kill him."

Lupin hissed. "It would be a disgrace to Peter's memory if I were to shrug that comment off but it's more than my job's worth."

Black laughed bitterly. "You'll see, Remus. You won't like it but you'll see."

The sun was rising and Lupin deemed himself safe enough. He turned on his heel, still clutching his wand and listening intently for signs of pursuit. He risked a glance back and the dog was sitting in exactly the same place, waiting patiently.

Yes, he'd gone completely mad. The sensible thing to do was report him and admit to breaking Dumbledore's rules as a teenager, endangering every student in the school. Lupin shuddered. No, he couldn't do it. Besides, what threat was Black? He seemed intent only on killing a dead man.

"Quite mad," Lupin muttered, wondering whether he was referring to Black or himself.

He had the suspicion that Harry might comfort Hagrid. Their relationship was such that it was only to be expected. He pulled out the map and watched, knowing that Harry's route would lead him towards the Forbidden Forest. If Black decided to take his chances, he would regret it for the remaining four minutes of his life.

Lupin pulled out the map and for the first time in sixteen years, uttered their code or password as Black had preferred to call it.

What he found made him forget how to breathe. His hands shook as he pushed his fringe back.

His own handwriting in bright green ink labelled the figure who was currently trapped in a pocket that was dangerously close to the jaws of Sirius Black.

Peter Pettigrew

He reached for his wand and sprinted out of his office, knocking over the smoking goblet on his way out.

The puzzle piece finally slotted into place. They had switched. Sirius had thought him the spy all along and it seemed they were both owed an apology.

As for Peter Pettigrew, Sirius Black would be the least of his worries.