How would you like to see the set of the soon-to-be hit movie Heat Wave? All in due time. First things first. Beckett's ex-partner Mike Royce is back, though not for long. He's being hunted by an assassin. Moments before the killer fires a fatal shot, Royce says, "You have no idea the hell that's about to rain down on you." We can only assume he's talking about Beckett.
Royce had just flown into town from L.A. A mystery man also came in from the City of Angels for a grand total of six hours-just enough time to kill Royce. Beckett is shut down when she asks to investigate out west. It's not going stop her from using vacation time to go on her own. That doesn't mean she's going alone. Castle booked her a first class plane seat right next to his. Hey, they've been after him to visit the set of Heat Wave anyway.
Castle convinces Beckett to stay at his complimentary two-bedroom suite. He tells hotel manager Maurice to cancel the couples massage. He and Beckett are here to work. They visit one of Royce's clients, Gene Simmons. The KISS legend points Castle and Beckett to a beautiful wannabe actress named Violet Young. She happens to be shooting a commercial at the same studio where they are filming Heat Wave. How fortuitous!
Castle and Beckett come across a couple of Ryan and Esposito clones while on the movie set, but Violet Young is nowhere to be found. They break into her apartment only to be busted by the local police. Detective Kyle Seeger (guest star D.B. Sweeney) doesn't want a rogue cop running around his city. Neither does Captain Montgomery. He orders Beckett to return home. Yeah, that's not gonna happen.
Castle and Beckett discover Violet Young was an unwitting pawn used by some bad guys to get close to Charles Kelvin, a man whose company is producing dissolving bullets. Back in New York, Esposito and Ryan obtain a photo of the killer though airport security. He has a partner who is in town searching for Violet. Back in L.A., Castle and Beckett have a heartfelt exchange of warm words in their hotel suite. But at the end of the night, they begrudgingly retire to their separate bedrooms. So close, yet so far.
The next day, Castle and Beckett use some Heat Wave movie magic to glean some info from the security guard who assisted in the theft of the dissolving bullets from Charles Kelvin's place. They learn the killer's real name is Russell Ganz and his partner is Donald Mannis.
Maurice the hotel manager points Castle and Beckett towards the man they seek. Ganz is trying to find a buyer for those bullets while hanging poolside at their hotel. Time for a little undercover work. Actually, Beckett isn't covered at all as she rises from the pool in a sexy swimsuit. She makes contact with Ganz, but blows the deal trying to protect Castle.
Back in New York, Ryan and Esposito save Violet before Mannis can gun her down. In L.A., Beckett calls Detective Kyle Seeger for a little hometown backup. They thwart the buy for the dissolving bullets. As for Ganz, Beckett tracks him under the Santa Monica pier. She has him down on the sand, gun pointed at his head. She could easily kill him, but that's not Kate Beckett's way.
While checking out of the Beverly Hills hotel, Castle presents Detective Seeger with a swell complimentary robe. As for Beckett, she uses the plane ride home to read a letter Royce left behind. It's not about the case. It's about her and Castle. Royce doesn't want Beckett to put the job ahead of her heart. He doesn't want her to look back on her life and think "if only." As Beckett looks over at her sleeping partner, we're left wondering if she'll take this advice to heart.