Castle - Season 3 - Eps 6: 3XK
When a beautiful woman is found dead in an alley, all clues point to her being a victim of the notorious Triple Killer. The Triple Killer, or 3XK, terrorized New York City four years ago, then mysteriously disappeared. Now he's back. In a deadly battle of wits, Castle and Beckett race against time to stop 3XK before he claims his next victims.
About Castle

Title: Castle
First Air Date: 2009-03-09
Last Air Date: 2016-05-16
Status: Canceled
Rating: 7.997/10 (from 1924 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