Peter Pettigrew's hiding place was empty. There was no sign of a struggle.

"Wormtail, what have you done?" Sirius muttered. But he already knew the answer.

Sirius had arranged to check that Peter was safe, that night.

Well, Peter was safe. But not for long. Not when I'm through with him.

He would have just apparated to Godric's Hollow, but he couldn't leave his flying motorbike at Peter's ... whatever he called this dump of a place.

The sun glowed upon the roof of James and Lily Potter's house, defining the caved-in portion with a deep shadow. The room that was baby Harry Potter's was blown apart, Sirius could see it from the street.

Shaking, Sirius opened the gate into the yard, silently. Curse that silent gate, they might've had some warning if it had creaked.

The front door was open, James Potter lay in the doorway, dead. Upstairs, in the nursery, Lily was lying dead as well. A giant of a man, twice as tall as the average wizard and four times as wide, was cradling baby Harry in his vast arms. Harry was crying. Harry was alive.

"What are you doing here, Hagrid?" Sirius addressed the giant.

"Come to pick up Harry," Hagrid said. He gave Sirius a consoling pat on the back as though to comfort him over his best friend's death.

"Give Harry to me, Hagrid, I'm his godfather, I'll look after him."

Hagrid shook his vast head. "Dumbledore says I'm ter take him and meet at some Muggle address where his aunt an' uncle live. He's goin' ter live with them now."

"James and Lily made me Harry's godfather, Hagrid. They wanted me to take care of Harry if anything happened to them. And —" Sirius gestured to the room, leaving the 'something happened to them' unsaid.

"Can' give him to you," Hagrid maintained. "I've got orders from Dumbledore."

"Fine. You can take my motorbike then, it's parked outside, I won't need it anymore," Sirius handed Hagrid the keys and disapparated.

He was going to kill Peter for what he'd done. He would of course be sentenced to life in Azkaban prison for murder once he did, but the traitor would be dead.

Peter was in a crowded street, packed with Muggles. He hid his hands behind his back, and Sirius caught a brief glimpse of his wand. "Lily and James, Sirius! How could you?" he shouted in a fake sob for the whole street to hear. Peter had always been good at acting.

"How could I ? Betray Lily and James Potter? Who do you think I am, you?" Sirius reached into his pocket for his wand.

Before he had even thought what spell to use, there was a great 'BANG' and a cloud of dust obscured his vision. Water sprayed up from a pipe in the newly formed crater in the street as the dust cleared; a rat scurried into the sewer. A heap of robes lay where Pettigrew had been standing, topped with a bloody finger. Peter must have cut it off himself in an effort to fake his death.

How fitting, the rat, the spy for Lord Voldemort, was the man with the ability to transform into a rat. Sirius, never one to cope well with dire circumstances, couldn't help but laugh at the observation.

He was still laughing hysterically when the first wizards from the Ministry of Magic arrived, and he finally took in the scene. About a dozen innocent Muggles dead, Peter Pettigrew's abandoned robes, wand, and severed finger in front of Sirius, holding his own wand and cackling. To everyone but Sirius, it looked like he had just killed Peter.

One of the Muggles was being asked what happened.

"— and then he pulled out a stick from his pocket and there was this explosion and the other guy was gone!"

"Expelliarmus!" shouted one of the Ministry wizards, and Sirius' wand flew out of his hand.

Another wizard did a silent spell and Sirius' hands were bound behind his back.

But he hadn't managed to kill Peter.

And the Muggles had just heard Peter shout that Sirius had betrayed the Potters.

"No!" Sirius shouted, coming to his senses just enough that the gravity of the situation was starting to sink in. "I didn't kill him, he faked his death, he's a rat — literally and figuratively — he's an Animagus, he transformed into a rat and cut off his finger —"

"This one's mad," said another Ministry wizard, grabbing Sirius from behind and dragging him over to the others. "Straight to Azkaban for him?"

Sirius shook his head violently. "I'm innocent! I deserve a fair trial!"

One of the younger wizards of the group was nodding. "It's only fair. Everyone gets a trial. Even the Death Eaters we've caught got trials."

Sirius heard a sigh from behind him and a reluctant "All right."

The courtroom was dimly lit, underground, windowless; the bracketed torches in the walls cast odd striped shadows on the floor and the faces of the wizards who would be questioning him. Rows of benches rose in tiers above, seating the varyingly important wizards, all positioned so that they had a clear view of Sirius in the chair to which he was now chained by the arms.

A wizard by the name of Bartemius Crouch sat near the middle, reading the charges against Sirius while a scribe off to the side wrote everything down.

A small vial of some transparent liquid was brought out.

"Sirius Orion Black, do you consent to drinking this Veritaserum, otherwise known as the strongest truth potion in current knowledge, to verify that your answers are entirely correct? The consumption of truth potion without the drinker's knowledge being illegal, you will not be forced to accept it but further doubt will be cast on your responses. Being fully aware that other secrets you may be hiding may be revealed should they be relevant to the story that your explanation requires." Crouch's frown deepened at the last sentence as he spoke it, he clearly thought any secret worth keeping was also worth a sentence in Azkaban.

Sirius nodded.

He drank the scentless, tasteless potion in one gulp and Crouch began his questioning.

"To get straight to the point. Did you kill Peter Pettigrew?"

"No. But I meant to. Stupid rat got the best of me."

"You planned to kill Pettigrew?"

"Yes."

Crouch glanced around at the others as if asking whether they should end the trial now. Many of them shook their heads.

"Peter Pettigrew claimed you to have betrayed the Potters to He Who Must Not Be Named, making you responsible for their deaths," Crouch went on. "Do you deny it?"

"Yes, I deny it. I would have died before I betrayed them."

"Were you not the Potters' Secret Keeper when they decided to hide their house under the Fidelius Charm?"

"I convinced them to change to Pettigrew at the last moment. I would be the bait, Voldemort —" the entire room seemed to shiver at the name. "— would come after me, not expecting us to use such an inept wizard. If the Death Eaters expected me to be Secret Keeper, Peter would be safer. Who would attack a useless lump like him? We didn't tell anyone, there's been a spy for Voldemort in our midst for a year now and we didn't want to alert the spy that there had been a change of plans. We never imagined the spy would be Peter. Must've been the best moment of his life when he got to tell Voldemort everything."

"Will you please stop using You-Know-Who's name?"

"No."

"You claim Pettigrew faked his death, then? By transforming into his Animagus form? You claim Pettigrew is an unregistered Animagus?"

"Yes. He's been able to transform into a rat since we were fifth-years at Hogwarts."

"And yet you claim he is an inept wizard?"

"He needed all the help he could get in the transformation for years."

"You've known he was an Animagus for six years, and never turned him in. Why?"

"I suppose it was because I couldn't think of a situation in which I am not also condemned for being unregistered."

"You are an Animagus too?"

Sirius sighed internally. To clear his name he had to confess to a crime. "Yes."

"Very well, that's all. You are sentenced to six months in Azkaban for attempted murder and failing to register as an Animagus, however should you register as an Animagus — and perhaps help us to track down Pettigrew — we may  shorten your sentence."

There was an announcement put out that Peter Pettigrew was now wanted by the Ministry for the mass murder of twelve Muggles, becoming an Animagus illegally, and his involvement both with Voldemort and in the murder of James and Lily Potter.

Sirius registered with the Ministry as an Animagus. He simply had to tell (and show) them which animal he transformed into so they could write down his distinctive features. A few got quite a fright when he transformed into a bear-sized shaggy black dog, thinking they had seen the Grim, a death omen. No specific dog breed could be identified, so one even suggested they simply write that his animal form was the Grim.

Azkaban prison was like hell on ice. The guards, dark creatures known as Dementors, filled the place with a chill that ran deep in the hearts of anyone around, forcing them to relieve their worst memories in their minds, sucking every happy thought or remotely positive feeling from them, leaving the prisoners with only their worst experiences of their lives and the worst feelings possible. Six months would have been torture. Most prisoners went mad within weeks, even days of being there.

Leaving Azkaban was the complete opposite. As Sirius stepped out, all of his happy memories came flooding back to him. It might have been the best experience in his life.

But he would never forget.

(Sorry I don't know how trials work. I'm just somewhat copying what happened in the Goblet of Fire and Order of the Phoenix books. And I just picked a random amount of time for him to be in prison for. Considering this prison has Dementors, I think six months is fair enough for attempted murder.)