Molly Quinn is a 'Blue Butterfly'

Molly Quinn goes back to the 1940s in this new still from Castle.

In “The Blue Butterfly,” when Castle (Nathan Fillion) and Beckett (Stana Katic) 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.

“The Blue Butterfly” premieres Monday, February 6th @ 10PM ET/PT on ABC.