When Castle and Martha are taken hostage by a crew of bank robbers dressed in hospital scrubs and using classic television doctor names, Beckett finds herself on the outside, desperately trying to rescue them -- which proves to be even more difficult with a by-the-book hostage negotiator watching her every move. Castle becomes the de facto leader of the hostages, which includes Barry Livingston, and discovers that the robbery is actually a skillfully orchestrated distraction for an even more sinister plan. But with Castle stuck on the inside and Beckett on the outside, will either be able to foil the bank robbers' plans before it is too late?

Sniper on a killing spree is terrorizing New York City. With the clock ticking down to the next murder and nothing to go on except a killer with no apparent motive but to instill terror, this could prove the team's toughest case yet. The hunt is made even more complicated when Beckett begins to experience increasingly strong moments of PTSD - moments she tries hard to hide from Castle and the detectives.