TV Castle - Season 4 Episode 21 : Headhunters Castle - Season 4 Episode 21 : Headhunters 7.975/10 by 2009 users With tensions rising between Castle and Beckett, Castle finds himself a new partner -- Detective Ethan Slaughter (guest star Adam Baldwin, "Firefly"), a tough and colorful cop from the city's gang unit. But Castle gets more than he bargained for when Slaughter shows him a grittier side of police work that puts Castle in the line of fire like never before Details Casts Posters Images Title Castle - Season 4 Episode 21 : Headhunters Alternative Titles Касъл, Castke, Κάστρο, کسل First Air Date 2009-03-09 Last Air Date 2016-05-16 Number of Episodes 173 Number of Seasons 8 Genres Drama, Crime, Networks ABC, Casts Nathan Fillion, Stana Katic, Molly C. Quinn, Jon Huertas, Seamus Dever, Susan Sullivan, Tamala Jones, Toks Olagundoye Plot Keywords , Richard Castle Nathan Fillion Kate Beckett Stana Katic Alexis Castle Molly C. Quinn Javier Esposito Jon Huertas Kevin Ryan Seamus Dever Martha Rodgers Susan Sullivan Lanie Parish Tamala Jones Hayley Shipton Toks Olagundoye Episodes List Castle Season 4 :Episode 1 Rise Rise 2011-09-19 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 2 Heroes & Villains Heroes & Villains 2011-09-26 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 3 Head Case Head Case 2011-10-03 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 4 Kick the Ballistics Kick the Ballistics 2011-10-10 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 5 Eye of the Beholder Eye of the Beholder 2011-10-17 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 6 Demons Demons 2011-10-24 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 7 Cops & Robbers Cops & Robbers 2011-10-31 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 8 Heartbreak Hotel Heartbreak Hotel 2011-11-07 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 9 Kill Shot Kill Shot 2011-11-21 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 10 Cuffed Cuffed 2011-12-05 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 11 Till Death Do Us Part Till Death Do Us Part 2012-01-09 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 12 Dial M for Mayor Dial M for Mayor 2012-01-16 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 13 An Embarrassment of Bitches An Embarrassment of Bitches 2012-01-23 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 14 The Blue Butterfly The Blue Butterfly 2012-02-06 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 15 Pandora (1) Pandora (1) 2012-02-13 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 16 Linchpin (2) Linchpin (2) 2012-02-20 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 17 Once Upon a Crime Once Upon a Crime 2012-02-27 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 18 A Dance with Death A Dance with Death 2012-03-19 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 19 47 Seconds 47 Seconds 2012-03-26 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 20 The Limey The Limey 2012-04-02 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 21 Headhunters Headhunters 2012-04-16 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 22 Undead Again Undead Again 2012-04-30 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New... Castle Season 4 :Episode 23 Always Always 2012-05-07 After a serial killer imitates the plots of his novels, successful mystery novelist Richard "Rick" Castle receives permission from the Mayor of New...