When a Japanese ballet dancer is mysteriously murdered, Castle and Beckett's investigation into her secret life uncovers evidence that she was killed by a ninja, and now that ninja is coming after them.

When construction workers find the body of an infamous New York mobster who disappeared in the seventies, Beckett and Castle try to solve this three decade-old Mafia hit. Unfortunately, their only witness is a man who thinks it's still the 1970's, so to uncover what he knows, they must play into his delusion, and party like it's the last days of disco.