Kick the Ballistics

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.