Last season ended with Beckett wrestling over whether to take a high-profile job in DC -- a dilemma made more complicated when Castle proposed to her. In the Season 6 Premiere of "Castle," Castle and Beckett will deal with the consequences of their decisions against the backdrop of a high-stakes investigation.

Continuing from the season premiere episode, Beckett races against time to find a stolen toxin capable of killing tens of thousands of people. To make matters worse, Castle was exposed, leaving him with less than 24 hours to live.

With Beckett still in D.C., Castle and the boys investigate the murder of former child star Charlie Reynolds, who rose to fame playing the lovable nerd on an early 90s High School sitcom. But the case takes a turn for the strange when Agents Beckett and McCord arrive from Washington to take over the investigation, creating competitive tension in the precinct. But why would a washed-up actor's death warrant Federal scrutiny? Whatever the reason, Beckett and McCord aren't telling. Meanwhile, Castle has to contend with a new face at the 12th, NYPD Detective Frank "Sully" Sullivan.

A desperate young murder suspect, Emma Briggs, takes hostages at gunpoint then mysteriously insists that she will only negotiate with one person: Richard Castle.

A grisly murder investigation leads Castle and Beckett to a suspect who claims he's traveled back in time to stop terrible events from unfolding, events that will change the course of human history. Is he simply a deluded killer, or is it possible that he's telling the truth?

As Castle and Beckett investigate the ritualistic murder of a young woman, they find strange symbols in the victim's apartment; Castle struggles with Alexis' decision to move in with Pi.

Alexis enlists Castle’s help on an Innocence Review case to prove that a death row inmate, Frank Henson, was wrongly convicted. With only 72 hours left before his execution, Castle and Alexis (with help from Beckett) urgently investigate the original murder, only to uncover explosive secrets that may seal Frank’s fate.

When a famed relationship therapist is murdered, it appears that her access to the secrets of her elite and powerful clients led to her death. But when Castle and Beckett discover the victim was in possession of a rare object worth millions of dollars, they realize that this case may be even more complicated – and dangerous – than they thought.

Castle and Beckett arrive at a crime scene to discover that the female victim bears a shocking resemblance to Medical Examiner Lanie Parish. As the team tries to make sense of this mystery, they realize the killer may be targeting detectives of the 12th Precinct. Dr. Kelly Nieman, an exclusive Manhattan cosmetic surgeon who draws Castle and Beckett's interest because of her connection to the victim.

Before dying, he hands a mysterious bundle to the priest. When the bundle turns out to be a smiling baby boy, Castle and Beckett find themselves accidental nannies to the newborn. But when they determine the baby and the victim were not related, they discover that finding his rightful parents may be just as hard as solving the murder.

When Castle and Beckett discover that the victim of a building fire was actually shot to death, they get on the trail of a serial arsonist turned murderer. Meanwhile, Ryan's wife, Jenny, goes into labor, but disaster threatens to ruin the joyous moment.

The murder of a young video store clerk takes a strange turn when the team discovers his past history as a high-level hacker. But it's nothing compared to the shock Castle receives when their investigation leads them straight to his father, Jackson Hunt.

When a pop star is found dead in an alley, Beckett and Castle look into her hard-partying lifestyle; a shocking revelation rocks the investigation.

Castle og Beckett etterforsker drapet på en ung jente som ser ut til å ha blitt drept med telekinese. Saken har mange likheter med skrekkfilmen «Carrie».

En ung kvinne tilstår drapet på en skuespiller, og det kan se ut til at saken er klappet og klar for Beckett og Castle. Men da de avdekker spor som tyder på at den mistenkte overhodet ikke er morderen og en annen person avgir en like overbevisende tilståelse, innser teamet at saken er mer mystisk enn de trodde.

Beckett blir spurt om å hjelpe til i en narkosak, men et mislykket undercover-oppdrag setter livet hennes i fare. For å overleve må Beckett håndtere noen av de farligste mennene i New Yorks underverden, deriblantt en mektig fiende fra hennes fortid.

En japansk ballettdanser blir drept på mystisk vis. Castle og Becketts etterforskning av hennes hemmelig liv avdekker bevis på at hun ble drept av en ninja, og at ninjaen nå er ute etter dem.

Castle og Beckett etterforsker drapet på en aksjemegler. Saken tar en sjokkerende vending når de oppdager at offeret jobbet for statsadvokaten, som viser seg å være Gates' ukjente søster.

Når bygningsarbeidere finner liket til et beryktet mafiamedlem som forsvant på 70-tallet, må Beckett og Castle løse et 40 år gammelt mafiadrap. Det eneste vitnet tror at han fortsatt lever på 70-tallet, så for å finne ut hva han vet, må de feste som om det var diskoens siste dager.

En fremadstormende profesjonell skateboarder blir skutt og drept av en mystisk motorsyklist. Castle og Beckett undersøker ekstremsportmiljøet, der det ikke bare er halsbrekkende øvelser som er farlig.

Becketts hemmelige etterforskning av drapet på moren går galt når en mann hun har overvåket blir drept. Før hun vet ordet av det, havner hun og Castle i både politiets og senator Brackens søkelys.

Castle og Becketts etterlengtede bryllup er bare dager unna. Men når de kommer over sjokkerende opplysninger, kastes de ut i en vill jakt fylt av maskerte menn, motorsykkelgjenger og en av Becketts tidligere flammer.