Season 4 Episode 14

full size Beckett and Castle in Season 4, Episode 14: “The Blue Butterfly”
Credit: Karen Neal/ABC Television Group © 2012 Disney

Title: The Blue Butterfly
Air Date: February 6, 2012 at 10:00 PM PST

When Castle and Beckett investigate the killing of a treasure hunter, they discover the case is linked to a mysterious homicide from 1947 involving a hard-boiled private detective. Castle realizes the only way to solve the present-day murder is to solve the murder from the past. The 1947 case comes to life through stylized flashbacks, featuring Castle as the private eye and Beckett as a femme fatale.