Valkyrie

(Part 1) Beckett accepts Castle's marriage proposal, before moving to Washington DC for her new job, where she begins training and meets her new partner, Rachel McCord (Lisa Edelstein). After 6 weeks apart, Castle surprises her at her apartment, where he causes some trouble when he attempts to help her with a classified case. Castle returns home to discover that Alexis has brought a new boyfriend, Pi, back from her trip to stay with her, but is soon taken into Federal custody, where Beckett tells him he was exposed to a deadly chemical agent and has only one day to live.