Dumbledore stood outside the once-quaint cottage in Godricks Hollow and felt a pang deep inside his chest. He had known that a fidelius wasn't enough, but James and Lilly had disagreed. The whitewashed walls were blackened around the edges of the explosion, and the wards that had survived were struggling under the heavy pressure of the residual magic.
Bolstering himself, he stepped inside, spotting James lying at the bottom of the stairs. Fearing the worst, he strode over and felt his pulse, finding nothing. His hands were shaking slightly, but no pulse did not necessarily mean death. Casting a diagnostic charm over James, Dumbledore was relieved to see that he was alive, though under a magically enforced artificial stasis not unlike the Draught of Living Death. Immediately, he frowned. Why would Voldemort go to the lengths of breaking the Fidelius if he wasn't going to kill the Potters?
He climbed up the stairs with trepidation, his lithe movements odd for someone his age. In the doorway of the nursery, he saw Lilly similarly indisposed, lying prone on the floor. Stepping over her, he saw two identical cots with two very similar children sleeping; the only difference was a bright, silvery scar unnaturally placed on the younger twin's forehead. On the floor in the middle of the room was a pile of robes, the body that used to inhabit them nowhere to be seen. Laying next to them was the wand that had been used to commit the crime.
Dumbledore steadied his heartbeat with the trained ease of a high-level occlumens and quickly analysed the most probable solution. Voldemort had snuck into the Potter's Cottage that James, Lilly, and their two sons inhabited. This was likely due to the prophecy, the one that Voldemort had only heard half of. The frown that remained on Dumbledore's face deepened. He had hoped to have some time before the next part of the prophecy became apparent, but unfortunately, it appeared he didn't have that luxury.
and the Dark Lord will mark him as his equal…
The rune on young Harry's forehead that had dimmed slightly was likely that mark, but he had never seen anything remotely similar to it, neither in shape nor colour.
An idea striking him, he cast Prior Incanto at the dropped wand, and only three ghostly images emerged from the tip. The first and most recently cast was a bright green flash that still managed to instil terror in the old man, even though it was just in memory form. The next was a red spell that he didn't recognise; it looked much like Stupify, though unusually tinged with darkness. Perhaps the most worrying of all, however, was the first that had been cast within the past hour, Defodio, the gouging charm. Used for little other than forming runes, it gave little indication of what He-Who-Must-Not-Be-Named had been planning. Any half-formed runes that had been cast with dark intention may take an unwilling sacrifice if a willing one is not provided, and that meant the area was far more dangerous than he had previously assumed.
A roar from outside was the telltale sign of Sirius Black's arrival. Dumbledore straightened and turned, ready to confront the man who had sold the Potters to Voldemort.
There was a loud cry of grief from downstairs, and a cold hand gripped Dumbledore's heart in a vice-like grip. It felt wrong, but there was no other option. Sirius Black had betrayed the Potters, and he must be punished. As the footsteps on the stairs grew louder, Dumbledore's hand tightened on his wand, and he readied an Incarcerous for as soon as Sirius appeared around the corner.
But it never came. Sirius let out a growl that sounded uncharacteristically like a dog's, followed by a faint whispering that only Dumbledore's magically enhanced ears would have been able to pick up: "I'll kill you, Wormtail; mark my words."
There was a crack, the anti-apparition wards having succumbed to the prior explosion, and carefully, Dumbledore exited the room and saw nothing. It didn't matter; the Aurors could chase after Sirius, his most pressing concern was the two boys and how one of them had survived the killing curse.