Castle and Beckett investigate the murder of a women found frozen and tangled in steel bars at a construction site. The case leads them to look into an old case and also has Beckett thinking about some memories of her past.

Castle and Beckett investigate the murder of a woman found drowned in motor oil in a motel bathtub. They seek the help of a true crime journalist who might have a connection to the victim.

Castle and Beckett investigate the murder of a missing plastic surgeon who is found dead in the front seat of his car after a week of being parked curbside. As they delve into the twisted world of surgery obsessed patients and secret operations, Castle experiences a fatherly rite of passage as Alexis attends her first prom. And while looking into Beckett’s past, he unearths information that could end his relationship with her forever.

When an Arctic explorer is killed during a polar expedition, the mysterious circumstances of his death take Castle and Beckett from the penthouses of Park Avenue to the halls of the CIA. But Castle's delight at the case's many twists and turns soon turns to frustration as he realizes that their elusive killer might just be fooling them all.

Castle and Beckett are thrust into the world of ex-cons and escorts. Meanwhile, Alexis has a private chat with Beckett about something that she's keeping from her father.

When Castle and Beckett are called to a wedding to investigate the death of a bridesmaid, Castle is stunned to discover that the soon-to-be bride is his old flame, Kyra, "the one that got away". Complications ensue as Kyra, caught off-guard by Castle's reappearance in her life, wonders if she's marrying the right guy. With the nuptials forestalled and the entire wedding party under suspicion, Beckett questions Castle's ability to be objective about the case. But when it looks to Beckett like Castle and Kyra might rekindle their romance, her judgment may be compromised as well.

Federal Agent Jordan Shaw, an insightful and accomplished Federal investigator teams up with Castle & Beckett to hunt down a cunning and elusive serial killer.

When Castle appears on a late-night talk show to promote his book, Heat Wave, legendary host Bobby Mann leans in during a commercial break and whispers, "They want me dead." When Mann dies later that night, seemingly of natural causes, Castle has to convince Beckett that there was foul play. During the investigation, Castle is seduced by a Hollywood hottie, who was the other guest on Bobby Mann's show the night he died.

When a coded document attracts Castle's attention, Beckett must steer the case back to the violent felons who populated their victim's world; when Beckett's ex-partner arrives, Castle must watch the relationship become romantic.

Castle and Beckett investigate the murder of an NYC subway worker found shot in Central Park. But, while investigating the murder they uncover the abduction of a young boy as well. The team must determine the motives behind the high stakes kidnapping in order to save the young boy's life.

Castle and Beckett investigate the murder of a dockworker turned bar owner who's body is found floating in the East River. In the process of the investigation they uncover a secret buried since the days of Prohibition.

A crew of bank robbers disguised as classic television doctors take hostages which include Castle and Martha. But things are complicated by the fact that Beckett's on the outside having her every move scrutinized by a hostage negotiator and Castle's on the inside with information that the hostages are just a distraction for a more ominous plan.

Castle and Beckett pursue a ruthless killer who, they discover, is part of a sinister, international conspiracy. Castle and Beckett are joined on the case by Sophia Conrad, a smart, sexy CIA operative who has a complicated past with Castle.