Watch Castle Season 4 Episode 21 online via TV Fanatic with over 6 options to watch the Castle S4E21 full episode. Affiliates with free and paid streaming include Amazon, iTunes, Vudu, YouTube Purchase, Google Play, and Verizon On Demand.
|YouTube Purchase||Watch Now|
|Google Play||Watch Now|
|Verizon On Demand||Watch Now|
It's a Firefly reunion on Castle this week, as Adam Baldwin guest stars in the fun role of Detective Ethan Slaughter.