Officer Nolan and officer Chen report to a structure fire and suspect that there is more to the situation than meets the eye. Meanwhile, after witnessing a sniper shooting, the team searches for the shooter and discovers that the perpetrator has a connection to one of their own.

When a new designer drug hits LA streets, it turns users into "zombies," and Officer Nolan and the team have a Halloween they won't soon forget. Back at home, Lucy questions whether her apartment building might be haunted.