A well-muscled man steps into a store and tries to hold it up. The cashier pulls out a shotgun, but the muscleman takes it away from him. Nash and the SIU arrive to find the muscleman holding four hostages with the shotgun. Nash and Joe go in: Nash pours soap on the floor; the muscleman slips; Nash knocks him out with a bag of ice. As Joe tries to cuff muscleman, muscleman stops breathing and dies.
The dead man is Bart Mackey, a local competitive body builder. Mackey is part of a rash of incidents involving body builders going amok and committing crimes. Nash suspects "high frequency" steroids. Evan checks out Bart's pager numbers. One of the numbers leads to steroid dealer Darrell Foley. But cop Jake Cage is already there beating up Foley. Nash and Joe intercede and save Foley. Foley reveals his drugs came from the Sutro Gym.
Jake Cage reveals that Bart Mackey was his brother-in-law. Jake is part of Fugitive Recovery, and a SIU reject. Jake even dated Caitlin once, taking her to a Monster Truck Rally. Nash wants Jake to go undercover at the Sutro Gym along with Harvey and Evan. But Jake deliberately blows Harvey and Evan's cover and gets them thrown out of the gym.
Nash and Joe intercept Jake on his motorcycle. They take him in the 'Cuda, but Jake spots an escaped felon from his armored suitcase full of mug shots. Jake jumps out of the moving 'Cuda and goes after the felon. They battle, with Jake bashing the felon with his suitcase and giant water bottles from a nearby truck.
Nash, Joe, and Jake go to see Spike, a female body builder who is wrestling two well-oiled men. She is hyper-aggressive on the steroids, as Jake and Joe join the fray. She fights them off, but Jake and Joe drag her to a rug, where Nash rolls her up into it. They take the rolled-up rug with Spike in it to the SIU. At the SIU, a much calmer Spike tells Nash that she got the steroids from Steve Pope, owner of the Sutro Gym and a chemist named Raif. Harvey and Evan wait at Spike's place for the call from Pope. She irons her clothes in a red bikini while broadcasting on the Internet. The call arrives - the drugs will be delivered 10 AM tomorrow.
Meanwhile, Cassidy has gone back to school. At street crossings, Cassidy has flashbacks of her auto accident. She skips class to see Evan, and impulsively wants to have sex in his truck. She says yes to Evan's proposal of marriage. But Evan is concerned that something is wrong, and he tells Nash that Cassidy is not herself. Evan doesn't want to marry yet under such circumstances. Nash decides to have Cassidy over for dinner to find out what's wrong.
Nash tells Caitlin to stall Jake while they go to the Sutro Gym. But Jake takes off, and confronts Steve Pope and his henchmen. They beat Jake up, but Nash intercedes along with Joe and Officer Ronnie. They all take on Pope's henchmen in a battle in the gym with barbells and training equipment as weapons. Pope gets away to his factory.
An interrogation of one of the henchmen reveals the location of Pope's factory. At the factory, Raif shoots Pope dead as he tries to make off with the stash of steroids. Evan, Harvey and Ronnie intercede and arrest Raif. At the SIU, Jake goads Caitlin into punching him in the eye. At Nash's apartment, Cassidy finally breaks down after seeing recently developed photos of her friend who died sitting next to her in her car.
For more, see commentary for Episode 70