Castle - Season 4 - Eps 14: The Blue Butterfly
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.
About Castle

Title: Castle
First Air Date: 2009-03-09
Last Air Date: 2016-05-16
Status: Canceled
Rating: 8/10 (from 1953 votes)
Language: EN
Seasons: 8
Total Episodes: 173
Network: ABC
Genres: Drama, Crime
Production Companies: Beacon Pictures, Experimental Pictures, ABC Studios, The Barry Schindel Company, MilMar Pictures
Synopsis
After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New York City to tag along with an NYPD homicide investigation team for research purposes.
Cast

Nathan Fillion
Richard Castle

Stana Katic
Kate Beckett

Molly C. Quinn
Alexis Castle

Jon Huertas
Javier Esposito

Seamus Dever
Kevin Ryan

Susan Sullivan
Martha Rodgers

Tamala Jones
Lanie Parish

Toks Olagundoye
Hayley Shipton