Andy and Gail go undercover as cocktail waitresses in a club known for drug trafficking; a young woman files a complaint against Dov; and Traci finds she still has feelings for Det. Barber, who's an old flame.
A full moon brings the crazies out as Andy and Swarek track a disturbed man while looking into the theft of three severed heads from a medical lab. Andy tries to protect a young woman who may be the next victim, and ends up putting herself and Luke in harm's way.
An informant's murder is investigated, and Gail's mother, Superintendant Peck (Lauren Holly), arrives to ratchet up the pressure to solve the case. Gail is assigned to protect the only known witness to the crime.
The division is quarantined when a suspect presumed drunk collapses due to an unknown disease. Elsewhere, a bank-robbery suspect is apprehended covered in blue dye, but the officers have trouble finding his violent accomplice; and Dov dates a bomb technician.
An undercover training exercise puts Andy, Dov and Traci to the test, and they cross paths with Swarek, who's on an undercover case of his own. Meanwhile, Dov faces a career-changing choice on a ride-along with a drug dealer.