The abandoned house stood on the dark edge of the cliff, the wood weathered and stripped bare. Derek entered cautiously, his gun drawn. The house creaked and groaned around him. Sounds of waves crashing against the rocks below echoed through the crisp night air.
There was a faint glow coming from the main room and Derek heard murmuring voices as he stepped closer. He pushed the door open, the hinges squeaked loudly enough to announce his presence.
They were sprawled out in the middle of the room, candlelight glinting off naked limbs. Stiles was straddling Theo's lap, and Derek watched as he raised himself and slowly sunk down again, Theo's cock disappearing into his ass.
Derek hadn't anticipated this. When he walked in he’d expected to find two serial killers hiding evidence, not casually fucking on the floor.
Theo grinned at Derek, his fingers curled over Stiles shoulder as the other boy rode him. "We've been waiting for you, Agent."
Stiles turned his head to grin at him, dark red blood splashed on his chest and smeared across his pale throat. He gestured to the corner, where a dark shape was slumped on the floor. "We did it, Der."
Derek stepped over to look at it, wooden floorboards groaning under his weight, and found his uncle's lifeless face staring back at him. Peter's throat was slit ear to ear, dark blood pooling around his body. Derek really couldn't bring himself to feel any sympathy for the person who had murdered his sister, even if he had been family.
It was finally over.
He holstered his gun and walked back to where the boys were still twined together. Stiles was smiling at him with that dark glint in his eye. The same glint that had first made Derek realise that the Sheriff's son was most certainly not what he seemed.
"He didn't even notice once I had him on his back," Stiles said, breathless, his voice hitching as Theo took the opportunity to thrust up. "He looked so surprised when Theo cut his throat. I wish you could have seen it."
Derek kneeled next to them, burying his face in the crook of Stiles' neck. He pressed an open-mouth kiss along his jaw, tasting sweat and the coppery tang of Peter's blood.
"You did so good. Both of you," Derek said, sliding a hand down Stiles' back to where they were joined, fingers tracing a path around the stretched skin of Stiles' rim. Both of the boys choked off moans as he slipped a finger into the tight heat beside Theo's cock. The feeling of Theo moving inside Stiles was exhilarating.
They were his now. Before, they had been adrift, killing aimlessly. He only needed to give them a push in the right direction, a purpose. The things these boys were capable of took his breath away.
Derek wrapped his other hand around Stiles' cock and stroked, coaxing out sweet little whimpers. Stiles tipped his head back and Derek sucked a bruise over his pulse point.
"Fuck," Theo thrusted up erratically as he came, fingernails scratching red lines across Stiles' skin.
Derek pulled Stiles into a sloppy kiss as he jerked him off, watching as come painted Theo's stomach.
"Derek," Stiles whined, grasping at him as Derek rose from the floor and straightened his clothes.
"We've already wasted enough time, both of you need to get out of here while I clean this up."
He'd already planted evidence in Peter's apartment. Enough to point to not only the murders Peter had committed himself, but to the ones Stiles and Theo had claimed as well. With any luck, nobody else would even realise there had been more than one active killer.
Stiles pouted and lifted himself off Theo with surprising grace. "You're no fun," he said, picking up his discarded clothes.
When they were dressed, Theo gave him a two-fingered salute. "See you around, Agent Hale. It's been good." He smirked as he walked out.
Stiles lingered, stepping forward to hook his fingers into the collar of Derek's shirt, and stared at him searchingly. "You better not forget about me."
Derek snorted, "Don't worry, you've left an impression."
Stiles grinned, bright and wicked, and curled a hand around the back of Derek's neck, pulling him into a harsh kiss. Stiles bit at Derek's lip hard enough to draw blood as he broke the kiss. "Good," he smirked, darting back in to lick off the blood. "Because, I've been told I should consider a career in law enforcement. Maybe I’ll see you around."
Derek brushed his thumb over the moles on Stiles' jaw. "I look forward to it."
He walked Stiles out to where Theo was waiting and watched as they drove away. He had no doubt he'd see them again, one way or another.
Derek breathed in the cool night air and glanced up at the stars. He fingered the box of matches in his pocket. It was time to finally put the last of his family to rest.