It appears Jerry Tyson a.k.a. 3XK has risen from the dead in tonight's episode of "Castle." Michael Mosley returns as the elusive serial killer to taunt Richard Castle (Nathan Fillion) and Det. Kate Beckett (Stana Katic), but his new identity may leave the crime-fighting couple stumped again.

Mosley last appeared on the ABC series two years ago when Castle shot his character off a bridge, causing him to fall 100 feet down into a frozen river. He'll reappear as a man who looks exactly like Tyson, thanks to cosmetic surgery, but claims to be someone named Michael Boudreau.

"I'd ask [the producers], 'Is this Jerry Tyson? Is this Michael Boudreau?'" Mosley tells Headlines & Global News about playing his new character. "They would just shrug their shoulders and give a little smile. So I would just play it as Michael Boudreau in those scenes."

The crime novelist never believed Tyson died in the shooting and linked his case to Dr. Kelly Nieman (Annie Wersching), a devious plastic surgeon that worked on two murder victims and made them look like Det. Javier Esposito (Jon Huertas) and medical examiner Lanie Parish (Tamala Jones) in an episode last season. Boudreau claims the good doctor also gave him the appearance of Tyson.

Wersching also returns in the two-part episode. Both actors knew their story lines connected when they met on set, but this will be the first episode they appear in together. The 36-year-old actor wouldn't reveal exactly how their characters will interact, but calls Wersching's performance "spooky."

The real drama will center on the cat-and-mouse game between Castle and Tyson that has played out over the last four years. Mosley believes his psychopathic murderer will continue to terrorize those around him until he's officially declared dead.

"I think the endgame for Tyson is chaos. His real last stop is Castle because he thinks Castle has a similar interest... he's equally fascinated by suspense and terror, but has a healthy outlet for it in his books. Whereas Tyson's fascination comes in acting out those impulses," Mosley says.

"I also think there's a ying and a yang to it. Castle's such a physically opposing but charming character, and I'm not. It's nice to see him unnerved by something. I don't think Tyson works without Castle."

The "Castle" two-parter starts tonight, Feb. 9 at 10 p.m. EST on ABC.

When he's not terrorizing Castle and friends, Mosley stars as the prickly EMT Johnny on USA's "Sirens." The show gave him the chance to return to comedy after he appeared in the last season of "Scrubs" on ABC.

"It's such a fun way to live," Mosley says about acting in a TV comedy. "You just go and crack up. The writers come over to whisper an alternate line in your ear and you try to say that as a trick to crack up the actor in front of you. The camera guy can't keep the camera straight because he's shaking from laughing. That's fun."

Now in season two, "Sirens" has found a rhythm that has allowed the show to expand its world and add new characters. Fortunately, the writing staff has worked well to accommodate all the players without sacrificing its main characters led by Johnny.

"If it was just Johnny there, I don't think people would like him. He is a cranky old grump sometimes, but because we have the energy that he can bounce off of other people, it works," Mosley says. "That crankiness bounces off Hank's (Kevin Daniels) pragmatism and Brian's (Kevin Bigley) innocence. We're kind of like Larry, Moe and Curly."

Also keeping Johnny in line is his off-again, on-again girlfriend Theresa (Jessica McNamee). The two have moved in together this season and are trying to keep the spark between them alive while growing comfortable with each other.

"As soon as you move in with somebody, you watch them brush their teeth and scratch their ass. Maybe it's not quite as exciting, so you have to try to keep that spark alive," Mosley says.

"Sirens" should have no problem keeping its spark alive with the many funny storylines set to air the rest of this season. The paramedic trio will have to figure out how to untangle a large snake from a woman's neck, convince a gangster (Steve Schirripa) to start eating healthier after a heart attack and help a rapper who's trying to gain street cred but shoots himself in the leg.

Johnny and Brian also have to chaperone a little girl's birthday party while Hank takes her mother to the hospital. "Johnny is a little put out at the beginning but by the end I think his heart warms," Mosley says.

"Sirens" airs on Tuesdays at 10 p.m. EST on USA.