In order to solve the murder of a treasure hunter Beckett (Stana Katic) and Castle (Nathan Fillion) are forced to solve a homicide from 1947 involving the same murder weapon, a private detective, a gangster (Mark Pellegrino), and a $1 million blue diamond necklace in the shape of a butterfly. The cast does double duty as both themselves and the characters in the private eyes memoirs as the search for “The Blue Butterfly” begins.
The hard boiled detective flashbacks are a hell of a lot of fun and it was fun to see how each character was recast to fit the narrative. Martha (Susan Sullivan) becomes the detective’s secretary, Alexis (Molly Quinn) becomes the client with ulterior motives, Beckett is the gangster’s girl, Ryan (Seamus Dever) and Esposito (Jon Huertas) are mob muscle, Lanie (Tamala Jones) finds herself as a lounge singer, and Castle, of course, casts himself in the role of the private eye.
Suspects in the current murder case include the victim’s business partner, a competing treasure hunter (Patrick Cassidy), a homelesss man, the old bartender (Chad Everett) of the Pennybaker Club, and the owner (Pellegrino) of a mysterious white Mustang with a very personal connection to the case, but to find the real killer Castle must connect the death of the PI in the 40’s to Beckett’s current case.
In the end it’s by solving the current murder that Beckett and Castle find out what really happened to Joe, Vera, and the blue butterfly. I’d have preferred if they had shot the flashback scenes in black and white, but the mix of the two cases, especially given the fun (if heavy handed) noir feel, makes “The Blue Butterfly” one of the show’s more memorable episodes.