Also to guest star on the May 2 installment of the show are Dominic Purcell, D.B. Sweeney and Jason George.
"While investigating the shooting death of her ex-partner in New York, Beckett comes to believe the suspect has fled to Los Angeles. Against orders, she travels to LA, going renegade to track down the killer, with Castle unexpectedly along for the ride," ABC said in a synopsis Monday. "As they dig deeper into the motives, they uncover a trail that leads from a rooftop pool in Hollywood to the sandy beach of Santa Monica. Along the way, they visit the set of the 'Heat Wave' movie (based on Castle's book) and enlist the cast to help break the case. But as they get closer to apprehending the killer, Castle begins to wonder whether Beckett is out for justice -- or revenge."
Purcell plays a local businessman who may have a connection to the slaying, Sweeney plays a detective in Robbery Homicide who questions Castle and Beckett about their rogue investigation, and George plays an entrepreneur with a connection to the homicide case.
"Castle" stars Nathan Fillion as crime novelist Richard Castle and Stana Katic as NYPD Detective Kate Beckett.