A rooftop sniper fires exactly thirteen shots leaving behind thirteen individually numbered shell casings. The SIU (Special Investigations Unit) responds, but two people are left dead and three injured. In addition, a police strike is on, forcing the SIU to respond to other routine radio calls.
Nash and Joe respond to a radio call of a public disturbance - a PCP drugged man is growling like a tiger inside a restaurant. During the struggle, Joe's Halloween costume for his baby girl is thrown on a stove and burned up. Joe must look for another hot in demand "Cuddle Bug" costume.
The rooftop sniper strikes again, firing thirteen shots at Evan and Harvey. The rest of the SIU responds, but the sniper gets away. Nash begins to suspect the sniper has special access to rooftops. Evan and Harvey respond to a radio call of an armed robbery. A dominatrix and her clients are robbed and handcuffed, but Harvey is confused about who to uncuff.
Headquarters is in chaos because of the strike. Pepe (Joe's former bartender) arrives and straightens things out such as the flood of phone calls and the roof leak. With the help of Pepe, Joe is off searching for a "Cuddle Bug" costume, but it turns out to be a wrong one - an imitation. Meanwhile Nash and Michelle check out the print shop of a militia group known as the Bay Area Patriots. The group is headed by Allen Tully, and includes member Carl Dugan, a veteran and former security guard for the building involved in the first sniper attack. Nash pressures the secretary of the militia group, Janey, to reveal the target of their next protest at the INS (Immigration and Naturalization Service) Building. The entire SIU sets up surveillance on rooftops. Michelle spots a man with a rifle and opens fire. On closer examination, the man is discovered unarmed with a window washer broom.
Michelle is suspended for shooting Brad Wilkins. Meanwhile, there is an eyewitness to another attempted sniper attack, which seems to prove Michelle did indeed shoot the wrong man. Carl Dugan meets Allen Tully, complaining that Dugan has caused the death of Wilkins. Wilkans is a window washer with key access to roofs - Dugan needed Wilkins' keys to the roof. Nash and Joe question the eyewitness and get a positive ID of Dugan and his T-shirt with "War Digest" imprinted on it. Through the "War Digest" magazine, an address of Dugan is obtained. Nash, Evan, and Harvey go to Dugan's address and discover Tully's body booby-trapped with a grenade. Michelle shows up with an illegally obtained file of Brad Wilkins' court-sealed Juvenile Records. The Juvenile Records reveal that Tully is Wilkins' foster father, proving a connection to Dugan and getting Michelle off the hook. Michelle also provides a list of Wilkins' list of building clients.
The SIU (minus the suspended Michelle) intercept Dugan at his next targeted building. Trapped in an elevator, Dugan feigns suicide. Wearing body armor, Dugan sustains many hits before he is finally brought down by Nash. The police strike is over, and Pepe leaves with his reward for helping out - a police uniform for intimate use on Halloween. Pepe has also gotten Joe his desperately needed Halloween costume. Michelle is restored to duty. Evan has a Halloween date with the dominatrix he helped out on the armed robbery.
For more, see commentary for Episode 38