It was months before he got another opportunity.
But this time Sirius had the cat.
It had taken time to build up the cat's trust. After months of roaming the grounds together, of Sirius sharing the rats he managed to catch, and the best spots for napping in the sun, and the darkest parts of the Forest to avoid, the cat finally began to warm to him. One night, when it began to rain, the cat curled up tight next to him inside a hollow log, and Sirius knew he'd done it. He'd never cared for cats, but this one was quite clever, and something about the way it trotted along, picking its paws up extra high so they didn't skim the grass, reminded him of James's cat. Merlin, he hadn't thought of that cat in years. Marmalade, was it? Yes. James called her little lady sometimes. He wondered what had happened to her.
Most likely dead along with the rest of the Potters.
As the cat grew more familiar with him, Sirius attempted to communicate. His attempts weren't perfect, Sirius's human intellect in a canine body at odds with the cat's feline patterns, but from what Sirius managed to gather, this cat lived in Gryffindor Tower, and his master was somehow associated with the Weasley boy in possession of Peter.
Need in, Sirius told the cat. Get rat.
Get rat, the cat agreed. Rat not right, not good. You get rat.
How? Sirius asked. He struggled to find the right words, words the cat would understand. Door locked. Need... key.
The cat flicked its plumy tail. I bring key.
It hadn't made any sense to Sirius at the time, but a couple days later, the cat arrived at the edge of the Forest with a parchment clutched carefully in his teeth. He dropped it at Sirius feet.
Key, the cat said proudly. Now you get rat.
Now the parchment was in Sirius's tattered pocket. It felt unsettling to be human again. He spent so few of his days human recently; living outside was not ideal, not comfortable, but his dog form made it infinitely more bearable. He could stomach the prey he managed to catch, for one thing, and the thick black pelt kept him relatively warm. Better than nothing, anyway.
The midnight castle was dappled in shadows and silence, and if his last creep through the corridors had felt eerily familiar, it was nothing compared to what the darkness was doing to his ghosts tonight. He didn't feel alone under these ceilings, not in the slightest.
"Back again, Padfoot?" James whispered as Sirius skirted across the dead Entrance Hall.
"I told you I would be," Sirius said.
"And I told you, you didn't have to." James tugged on Sirius's sleeve, and the two of them melted into a shadowy crevice as the Fat Friar drifted by.
"Shut up, Prongs," Sirius growled once the corridor was clear again. He wriggled out of his hiding spot. "You don't get to tell me what to do. You're not even real."
"No, I'm not," James agreed. "But does that really matter?"
Sirius ignored him. Tonight he was getting into the Tower, and not even James was going to stop him.
His path was sure in the darkness. How many times had he done this exact same thing? Taken these very routes? And he moved so much more quickly and quietly when he was on his own.
Before he was ready, he had reached the seventh floor. One more corner, one last corridor.
And there it was.
The entrance to Gryffindor Tower.
I'll be back. His own words ghosted around him.
Only...
"Who the hell are you?" Sirius demanded. His voice tore the silence.
The figure in the painting guarding the portrait hole jumped from sleep to attention.
"Hark! Who goes there? And at this wee late hour of the night?"
It was most decidedly not the Fat Lady guarding the entrance to Gryffindor Tower anymore. Sirius gaped at the replacement: a round minuscule knight, so small the dappled gray pony he'd been dozing against looked enormous by comparison.
The ridiculous little knight pushed the metal flap of his helmet out of his eyes to see better. It clanked almost immediately back closed. "Ah! A stranger! Stand ye and declare the password; otherwise, we fight!" He brandished his oversized sword. The swing nearly took him off-balance, and the action tugged at a distant memory, one involving the sixth floor, James, and a cauldron full of frogs.
"Wait a moment, I know you..." Sirius said slowly. "You're Sir Callum or some rubbish like that."
"That's Sir Cadogan to you, you insolent knave!" the knight said, indignant, now struggling to return his sword to the sheath. His arm was only just long enough to allow the point to catch properly.
"But don't you live on the sixth floor? What are you doing here? Where's the Fat Lady?"
Sir Cadogan, sword finally returned, drew himself up importantly. "Guarding common rooms is dangerous business these days, don't you know? My predecessor was attacked serving at this very post! Murderers run amuck, and I remain the only valiant soul around brave enough to take up the task."
So he, Sirius, was responsible for this.
He was surprised at how bothered he felt to know that his last visit had driven the Fat Lady away and left the Gryffindors to deal with this nuisance. It had never been his intention to ruin anyone's life beyond Peter's. Certainly not the Fat Lady's. It felt wrong to have removed her from her post where, as far as he knew, she'd resided since the beginning of Hogwarts. He'd hoped for a chance to apologize tonight.
Maybe it would make what he was about to do a little more okay.
"Turn around, Pads," James said softly.
"Right," Sirius said loudly, much too loud for the deserted corridor. He dropped his tone. James might be a hallucination, but beings like Filch and Peeves certainly were not. "The password." He pulled the crumpled, dirty length of parchment from his pocket and scanned the long list written there. It was the oddest assortment of nonsense he'd ever seen, but the cat had assured him this list would be his key to getting to Peter. "Um..."
"But what's this?" Sir Cadogan lifted his visor once again out of his eyes.
"Passwords," Sirius muttered. "I think. Only I don't know which one is right, there's a bunch here."
"And you believe one will grant you access to the Tower? Get you past Sir Cadogan the stalwart? Take your best stand, let's see how you fare!"
"Right," Sirius said, his eyes still trained on the parchment. Each word was more ridiculous than the last, but he had a feeling Sir Cadogan would hear him out; he seemed a lot more interested in challenging anyone just for the amusement of it than as an actual threat. Indeed, Sirius doubted the squat knight had any clue who he was actually talking to, that he, Sirius Black, was allegedly very dangerous. "Look, I'm just going to read them all off, and you tell me if I've got the right one." He cleared his throat. "Um... Oddsbodikans. Glabsast. Skrambagish." Sirius paused, wondering if Sir Cadogan was going to call him out for such gibberish, but he didn't. Instead, when Sirius looked up, he was leaning against his fat gray pony and nodding seriously.
"You seem very well-informed," Sir Cadogan said. "Perchance you've been spying, or have an informant on the inside, because while you have yet to give today's password, these all might have granted you access in the last few days."
"Really?" Hope, dangerous and hot, blazed to life in Sirius's chest. "Well, I have more, let me see." He dropped his eyes back to the parchment and started to read again, much quicker than before, the words dropping from his mouth like burning coals. "Bimfizzled. Axismus. Tarandiddle. Bathalith. Absquatulate. Fr-"
"But that's it!" Sir Cadogan exclaimed. "You clever mangy cur, you've done it!"
"I- I have?" He knew the cat said this would get him in, knew objectively there would be a correct password to open the way, but despite it all, despite the planning and waiting and watching and hoping, he thought he'd always be here, always remain in the corridor, looking for a way in.
"Indeed! Well done, good sir!"
And Sirius, frozen in shock, watched as the portrait hole swung open.