A half-naked woman is found in a park hanging by bondage cuffs and covered in caramel sauce. It's off to the underground world of sexual domination for Castle and Beckett to look for the killer.
Castle and Beckett investigate the murder of a dead man found in a family's house that just returned from vacations. Meanwhile, Castle is elected as one of New York's 10 most eligible bachelors.
While investigating the death of an Irish mobster, Beckett and Castle uncover a local turf war that may be connected to both a late-night infomercial guru and an international drug smuggling operation. But the case turns agonizingly personal when evidence emerges that the killer they’re chasing may have had a hand in Beckett’s mother’s murder.
Castle and Beckett are called to a wedding to investigate the murder of a bridesmaid. Castle realizes that the wedding is from a former girlfriend Kyra. Everyone's feelings are compromised, since Kyra has doubts about who she is marrying, Castle's feelings may not be as objective in the case and Beckett picks up the connection between them, making her a little jealous and have poor judgement.
Castle and Beckett investigate an art dealer that is shot in his gallery, but the bullet is inexplicably missing from the crime scene. To add to that, the only witness suffers from amnesia.
When a man is found dead stuffed in the garbage chute of an apartment building, Castle and Beckett have their hans full keeping the two women, who arrived afterwards to ID his body, from killing each other. During the investigation, it turns out the man was living a double-life.
Castle and Beckett investigate the murder of an Assistant District Attorney. Meanwhile, Alexis confides a secret to Beckett instead of her father.
After a bike messenger, carrying a package with content that is able to free a wrongly convicted man from pison, is brutally murdered, Castle and Beckett need to investigate the case. But they are surprised to find out that the tragic death is linked to another murder case previously investigated by Captain Montgomery. Now, in order to solve the new murder, Castle and Beckett must dig deep and discover all the secrets of a prominent New York family.
An up-and-coming rock star's body is found in a scene that appears staged from her recent music video.
It's close to Halloween, and a man is found murdered in a graveyard - with a stick through his heart, and sporting fangs. Castle and Beckett track the murderer to a vampire cult, all the while Castle is trying on costumes for his Halloween party - costume mandatory!