Picking up the morning after, Castle and Beckett now have to decide if they're a couple or was it just a onetime deal. But before they can tackle that, they must deal with those responsible for Kate's mother's death who are now a threat to Beckett.

While investigating the murder of a young woman, Castle and Beckett find evidence that links her death with Senator William H. Bracken (Jack Coleman), the man responsible for Beckett's mother's murder. Determined to finally bring Bracken to justice, Beckett soon realizes that things are far more complicated than they seem.

Beckett is recruited to assist on a Narcotics investigation, but a routine mission turns deadly when an undercover operation goes array. To survive, Beckett must engage in a battle of wits against some of the most dangerous men in the New York underworld – including a powerful enemy from her past.

A secret investigation conducted by Beckett related to her mother's murder goes awry when a man she has been surveilling is killed. When evidence links Beckett to the victim, she and Castle become the targets of a manhunt that puts both of them in grave danger.

After passing the Captain's exam last season, Beckett was surprised with an offer to run for State Senate. In the action packed season premiere, Castle and Beckett are adjusting to Beckett's career change, when a call from a mysterious stranger sets off an explosive chain of events. There are two sides to every story, and this unique two-parter will explore the same story from each of their perspectives, first from Castle's side as he searches for Beckett.

Beckett's side of her abrupt disappearance is revealed. After receiving a mysterious tip from her past, Beckett is launched into a fight for her life, with a team of mercenaries hot on her trail. While Castle investigates why his wife is on the run, Beckett must figure out who wants her dead, before they can finish the job.