Detective Santiago "Jimmy" Robertson is an investigator with the Los Angeles Police Department. From 2016 to 2018 he is part of the Hollywood division and is partnered with Rondell Pierce. His former partner Terry Drake was a prominent detective in the Robbery Homicide Division before his retirement.
Robertson and Pierce are assigned to investigate the murder of Edward Gunn. Robertson ties Detective Harry Bosch to the scene through fingerprints and a carved owl with an odd messages referencing his namesake, the Swedish painter. Robertson is concerned that Bosch will be protected from investigation by the rest of the squad as a well liked veteran. When Bosch becomes aware of the findings he clashes with Robertson. Robertson seeks advice from Drake who counsels that he should anonymously leak the findings to the press in order to ensure that Bosch's involvement cannot be covered up. Robertson goes to LA Times reporter Scott Anderson to leak the story.
Gunn's murder is ultimately revealed to have been carried out by retired detective Rudy Tafero, who planted the evidence incriminating Bosch. Robertson warily reconciles with Bosch and they work together to expose Tafero's involvement.
Robertson and Pierce are part of the task force investigating the murder of Howard Elias, led by Bosch. Robertson volunteers to work closely with Internal Affairs Sergeant Gabriella Lincoln on the case in order to keep an eye on her. Robertson and the taskforce ultimately expose Lincoln as a mole and link the high profile murder to Police Comissioner Bradley Walker.
Robertson requests and is granted a transfer to a Detective 3 position in Newton Division while working the Elias case. He crosses paths with his old colleagues from Hollywood Homicide squad when he picks up the case of the murder of Charles Fagan. Fagan was killed by drug distribution network enforcers after a car jacking. Working with Bosch, Robertson is able to tie the killing to an enforcer from the investigation who ultimately turns into a co-operating witness.