Castle senses a detective mystery manuscript found in the effects of a murdered modern-day treasure hunter is the key trough the jewel at stake, a blue diamonds-composed blue butterfly necklace. As the team works out the story situated in 1947 in the same now derelict music club, then Mahattan's place to be, involving murder, gangsters and theft, they work out the true parts and identities of culprits and victims. Written by
Did You Know?
After one of his fantasies, Castle asks Ryan to say "boyo" with an Irish brogue. The scene was written that Ryan only said it once; the back and forth volley of "boyo"s between Castle and Ryan was ad-libbed by Nathan Fillion
and Seamus Dever
. See more
The song "Istanbul (Not Constantinople)" that is playing is from 1953, and was not around in 1947 when the episode was set. See more
[as Vera, about the Blue Butterfly
... it's not a necklace, Joe, it's a diamond noose. And it's getting harder to breathe.
Then we gotta turn that noose into a lifeline.
Due to the nature of the episode, the usual music in the title sequence has been replaced with a jazz theme. See more
References Cagney & Lacey
Performed by Tamala Jones See more