The basement is cold, dark and damp, just what one would expect from the lair of a serial killer. The corridor is completely empty, but the doors leading to the cellars are surrounded by shadows and they'd be the perfect place for an ambush. Right now Castle is very happy that he missed the action, since the SWAT team has been in there before them and regular police has only been allowed to enter after the place has been secured.
They're carrying the killer out in a body bag as Castle and Beckett step through the metal door into cellar number five. They step aside to let the paramedics exit, and Castle notices that the body doesn't seem to fill quite all of the body bag.
"What happened to him?" he asks.
"He tried to blow up the whole building when he saw that he was surrounded," Beckett replies. She gets a flashlight from one of the agents, because there's no electricity down here and it's pitch dark. When she aims the light towards the walls, Castle gapes at the blood splatter.
"I'd say that his plan tragically backfired," he murmurs. The blood is still shining faintly in the light of their flashlights, and he can't stop staring.
Beckett puts a hand on his arm and he turns around, startled. "Come on, Castle, his other victims are probably still here somewhere," she says. Then she takes a good look at him and frowns. "Are you all right?" she asks.
"Yes, of course," Castle lies. He glances at the walls again, even though Beckett moved her flashlight and now the blood is hidden in the darkness. "Why wouldn't I?"
Her frown makes it clear that she doesn't believe him at all. "You're white as a sheet," she says. "And your one-liners are even worse than usual."
"My one-liners are the best," he replies, but it sounds weak to his own ears. He jumps when he hears footsteps, but it's just one of the crime scene guys carrying a large lamp. Loud noises have a weird echo down here.
When the lamp is lit, right at the center of the room, it almost blinds Castle. He shields his eyes with one hand and looks around. The room is sparsely furnished, just one metal table and a couple of cabinets in a corner. Its main feature is the blood on the wall. There's so much of it that Castle doubts it all came from the same person.
Everyone's shadows are projected on the wall and they move around like giants on a backdrop of crimson, or so he might tell Beckett. What he really thinks is that this room is very, very creepy. If he ever used it as inspiration in a book, he'd probably have to preface the whole thing with a reader discretion advised notice.
Beckett starts giving instructions on how to set the lamp and where to dust for prints and search for other evidence, but Castle has trouble paying attention. There's a locked trapdoor in the middle of the floor, and a couple of agents are busy getting it open.
"Castle," Beckett says, "go home."
"What?" he says, because he's been on his best behavior and she hardly ever kicks him out of crime scenes nowadays. "Why? I didn't do anything!"
"No, but you don't really want to be here," she says. "It's creepy, and it's about to get a lot more creepy if the bodies are really down there, and you're a civilian. You don't have any training for this." He starts to reply, but Beckett cuts him off. "I don't want your emotional scars on my conscience," she says, not unkindly. "You helped us catch the guy, there's nothing more you can do. Let the police handle the rest of this."
"Detective Beckett," one of the officers calls. "We're ready to open the trapdoor." Beckett's mouth is set in a thin line.
"Okay, then," Castle says. "But I'm not going home, I'll wait outside. I can cheer you up with my unparalleled sense of humor when you're done here."
"Your sense of humor is terrible," Beckett says. It might be a trick of the light, but for a moment her lips seem to curl upward. Then she straightens up. "See you outside," she says, and Castle makes his escape.