Michael Cudlitz plays John Cooper a seasoned Los Angeles cop, assigned to train young rookie Ben Sherman (Ben McKenzie). Cooper's honest, no-nonsense approach to the job leaves Sherman questioning whether or not he has what it takes to become a police officer.

Cudlitz and McKenzie are joined by other cast members, including Regina King, who plays Detective Lydia Adams. Adams lives with and is the primary caregiver of her mother. Her partner, Detective Russell Clarke (Tom Everett Scott) is an unhappily married father of three. Michael McGrady plays Detective Daniel "Sal" Salinger. Sal oversees fellow gang detectives Nate Moretta (Kevin Alejandro) and Sammy Bryant (Shawn Hatosy). Arija Bareikis plays patrol officer Chickie Brown, a single mom who dreams of being the first woman accepted into SWAT.