Synopsis

In the unsettling investigation of a young woman's fatal shooting, Castle and Beckett confront a detective's deepest fear. The weapon used in the crime is revealed to be Detective Ryan’s former service pistol – the very weapon pilfered by the serial killer known as 3XK. With time running out, the team must race against the clock to solve the murder, hunt down 3XK, and recover Ryan's gun before the killer claims another victim.