Old wounds are reopened when the retired lead detective on Beckett's mother's homicide case contacts her with new information, but then is gunned down right in front of Beckett before he can tell her what he knows. The investigation into his death leads back to a decades-old conspiracy that may hold the answer to who was behind Beckett's mother murder and why. With the stakes and emotions running high, Castle and Beckett take their partnership to the next level.