While investigating the mysterious shooting death of a young woman, Castle and Beckett face a cop's worst nightmare when they discover that the gun used in the killing is Det. Ryan's old service weapon - the one that was stolen by the serial killer, 3XK. Now with the clock ticking, the team must work to solve the murder, track down 3XK and retrieve Ryan's gun before the killer strikes again.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
Castle and Beckett investigate the murder of a young woman which was committed using Det. Ryan's old service weapon – the one that was stolen by the serial killer, 3XK. The victim's phone records reveal she had been in contact with Seth Carver, an undercover narcotics detective. When looking through old police records, Castle manages to find a link in the case which leads them to Philip Lee, the son of Clifford Lee, a notorious Chinese drug mobster.