Ghosts

After an accident leaves a young man dead, his spirit stays behind to warn his lover of impending danger, with the help of a reluctant psychic.

A series of drug-related hits leads the detectives back to the notorious drug lord Cesar Velez, who tried to kill ADA Alexandra Cabot. Alex returns from Witness Protection to assist with the case after the gun used in the murders is linked to Liam Connors, one of Cesar Velez's top agents.

While unusual circumstances are practically usual, a body drowned in a bathtub of motor oil has the team scratching its collective head. But the mystery only deepens when investigation shows that the victim may have been involved with a crime more than 20 years old and was working with a true crime writer. Behind the scenes, the relationship between Castle and Beckett finally rears its truly competitive head during a high-stakes poker game involving New York's legal system elite.