Sirius Black was a lot of things.

Reckless. (Yes.)

Harsh. (Undoubtedly.)

Arrogant.(C'mon, Evans, that's really a blow below the belt! You can't use my name as a synonym for arrogant! -Yes, Sirius, I can and I will.)

But nobody could say he was nothing but loyal to a fault. His Patronus and his Animagus forms were a testament to this truth. After all, dogs are the most loyal companions for humans.

So, when he found Peter's house empty and perfectly tidy, well, maybe not perfectly tidy, but as tidy as you could expect from Peter, his growing sense of dread was replaced by fear. He had to check the Potters, now!

He took his flying motorcycle and went as fast as he could to Godric's Hollow.

Please, they couldn't be dead, they couldn't, please. Maybe Peter went to sombody else's house. He would never betray them. If he had been kidnapped with a clever ploy he wouldn't talk, they were his brothers in all but blood. He would rather die than speak...

Seeing the house was like being punched, hard, in his guts and having the wind forced out of his lungs. He couldn't breathe. He entered the house running, being unable to wait another minute to have his answers. The kitchen was empty, maybe they had escaped, maybe...

Something black at the other side of the house, in the living room, attracted his attention. While he was advancing he realized it was a mop of unruly black hair. James' hair. He stopped, paralized by guilt and pain, hot white, threatened to engulf hid mind, driving him insane. He had to move, though.
He conjured a white sheet and, with a flick of his wrist, gently covered James' body with it.

The distressed cries of an infant reached his ears and a tiny part of him registered that he was flooded with relief. Harry had lived.
The sensation was short-lived, however; for when Harry cried, Lily would immediately hush him gently, singing a lullaby and rocking the baby in her arms until he fell asleep. He could't hear her singing a soothing tune. Nothing could have stopped Lily from comforting his child. Nothing, but death.

He would kill Peter.

He would torture him with the Cruciatus curse within an inch from insanity and then he would kill him, painfully and oh, ever so slowly.

He had escaped from home at sixteen, true, but he was the heir of the Ancient and Most Noble House of Black and, as such, he had been groomed from a young age to behave accordingly; tutoring in the Dark Arts included...

When Voldemort had made an attempt to recruit him, everybody had been shocked. He hadn't. Sometimes he wondered if his soul was fated to become as black as his name. Growing up in that household, that result wouldn't be abnormal, no, it would be typical; expected, even.
It appeared it was time to earn the family name, after all...

But first he must take care of his godson. He needed to comfort him and be comforted by him. Harry was the only thing he had left of his brother, and Slytherin be damned if he didn't everything in his considerable power to avenge the toddler now in his care. (And that's why your middle name is "Arrogant"! - Actually, Evans, my middle name is Orion...)
Walking up the stairs as quickly as he could, stepping over the debris littering the house, he finally reached the nursery, or, rather, what was left of it.

Lily's body was in front of the crib. She had died to protect her son and, in that moment, Sirius wowed to do the same. She was just out of reach for Harry, who hadn't stopped crying since she had died, probably. The baby's hand was still trying to reach her through the gaps of his crib. Sirius covered her body as he had done for James a few minutes previously, then he picked Harry up.

"Hush Prongslet,
don't cry no more,
now that uncle Padfoot is here,
You won't have to shed another tear,
Dark wizards cannot take you from my arms,
For my love for you won't let you come to harm,
So sleep tight and enjoy your dreams,
And when you'll wake up,
I'll be here with the Marauders,
To show you how to play...
Hush, now Harry James"

The lullaby didn't have the desired effect, but at least Harry had stopped crying.
Sirius remembered when he had come up with those rymes like it was yesterday...

Harry had been crying all night long and on and on for the whole morning. James and Lily were barely functioning, moving slowly to make lunch for the Marauders, baby Harry and themselves, like every other Sunday. When he arrived to Godric's Hollow, it was to find two zombies walking around, taking turns at holding a crying baby.

He could never stand Harry crying, not for the noise, but for the knowledge that if he cried he was in pain, or not completely comfortable. So he took him from the high chair and went in the livingroom where he sat on the couch and then proceeded to place Harry on one knee, bouncing him up and down, while making sure he couldn't fall. It usually cheered him up, but that time it didn't.
Then he used plan B. Harry was put on the floor, in a sitting position and Sirius shifted to Padfoot, proceeding to lick baby Harry's face. Then, he rolled on his back, so that the baby could lay down next to him, either pulling his fur, or using him as pillow.

It didn't work.

So he took the baby in his arms and started to sing different lullabies. When that failed too, however, he knew he had to employ drastic measures. Those measures consisted on coming up with this lullaby.

After he had sang those lines, baby Harry fell immediately asleep, and from that day on Harry wouldn't go to sleep unless sombody sang him Sirius' lullaby. The only variation Harry didn't mind was the substitution of "uncle Padfoot" with the title and nickname of the person singing the song, other variations where quickly dispelled, as Harry started crying if the lullaby wasn't sang correctly.

Sirius was brought back to the present when Harry tugged his sleeve.

"Unca Pa'foo?" Impossibly green eyes were scrutinizing his very soul, as if trying to find an answer for the question he wanted to ask.

"Yes, Prongslet?"
"Whe'e mama?"

"She has..." his voice broke. Merlin, Sirius, toughen up! "She has gone far away with daddy"
"When back?"
"Never...Harry, never..."

And the pain engulfed him, till everything left was grief, guilt and sadness. He couldn't bear it anymore. He cried untill his eyes were dry; he cried untill the numbness in his head covered the pain of having his heart feeling like it had been carved out of his chest, having nothing to fill the hole left inside.

Eventually, he calmed down enough to get out of the house that had begun to creak ominously; the danger of remaining there, and risking to be buried under the debris, made apparent by the obvious instability of the structure.

It was in the garden than Hagrid found them. Sirius was standing in front of the house cradling Harry to his chest and didn't register Hagrid 'so arrival until the latter put a hand on his shoulder. He turned slowly to greet the half giant, mindful of Harry who had just gone to sleep.

"Hagrid" Sirius inclined his head briefly.
"Sirius, I'm glad I found ya" answered the giant.
Hagrid glanced at the house.
"Are they...?"

The Marauder couldn't help inhaling sharply.
"Yes, they are. Listen, I have a job to do but I can't take Harry with me. I need to make sure he's taken somewhere safe first. Could you take him to Dumbledore?" Sirius was anxious to go, his voice impatient, laced with need and desperation.

"I cannot do that, Sirius. Dumbledore ask'd me to make sure ya were all right. Ya need to stay with 'arry."

"I CAN'T! " The anger inside Sirius abruptly exploded.

"IT'S MY FAULT THEY DIED! I NEED TO AVENGE THEIR DEATHS!"He wanted to shout more, to howl his grief at the uncaring skies, to make them listen to his anguish.

Harry's distressed wailing brought him out of it.

"An' what about little 'arry 'ere? Your the only one he's left! He's yer godson, it's yer duty to provide fer 'im!" Hagrid's firmness in the face of his anger made Sirius deflate a bit.

"I don't..I can't...I have other things to do, he'll forgive me, I'm sure."
"No he won't. Yer not going nowhere, Sirius Orion Black, D'ya hear me?"

Hagrid grabbed Sirius' arm - the one that wasn't holding Harry- and wouldn't let him go. Sirius was struggling like a wild animal who had been cornered and caged, desperately trying to escape. However, his movements were severely restricted due the fact that he was holding a sleeping baby and that the half giant wouldn't bulge.

At some point Sirius threatened to use his wand to get free, but Hagrid stubbornly refused to release his arm. He was far more resistant than a normal wizard, and he wouldn't be intimidated.
Dumbledore had tasked him with this mission and he would succeed. No matter what had to be done. His loyalty to the old wizard was unwavering.

"Are ya done yet? " Hagrid asked after a few minutes of uninterrupted struggle from Sirius' part.
That simple question seemed to switch something off inside Sirius and he abruptly stopped moving. He was simply too tired both physically and, most importantly, emotionally to continue.
"Good! I see you've come to yer senses."
"I'm a grown man, Hagrid, for Merlin's pants!" Sirius' anger was still palpable, but he wasn't shouting. He didn't want to awaken his young charge again. It didn't change the fact that he was now in a black mood. He had been denied his revenge...No, not denied...He still intended to haunt Peter; the reckoning had merely been postponed.

"You should have let me go! It was my right!" He muttered a token protest to avoid suspicion.
"Yeah, yeah, y'll thank me later, lad. Now, do ya mind helpin?"

Hagrid was tinkering with a metallic can, muttering things under his breath all the while touching the can with his umbrella. Whatever he was trying to do wasn't giving any results. Sirius took his wand, pointed it towards the can an said "Portus", reactivating the illegal portkey created by Dumbledore.

Apparently, that was how Hagrid had reached Godric's Hollow... Of course he had to use a portkey, Hagrid couldn't apparate to save his life...Well, it was too late now. The rat was sure to be already miles away. His first priority was to take care of Harry, as they would have wanted...

The portkey glowed blue and Sirius hastily reached to touch it.

Two silhouettes disappeared into the night, unseen by the people who, a hundred metres away, were celebrating Halloween.