After a meek city safety inspector survives being poisoned, he tries to help Castle and Beckett with the investigation.
Willis and Rox respond to an incident in the mountains of Los Angeles where a firefighter has been injured while fighting a wildfire, and the two decide to stay to look for a missing boy.
The murder of a Marine officer is linked to a former biker gang he joined while undercover for a year-long operation. Torres turns to old case notes and contacts to solve the mystery of the murder.