Marlo Cruz is a new Senior Officer who found no trouble making her new home at 15 Division. Ex-Swat, with nine years experience on the job, Marlo is no rookie. She’s smart, witty, and private, with an uncomplicated view towards life and relationships.
Marlo’s been at Divison 15 for three months when Nick and Andy return—bringing loads of unwanted drama with them. Her relationship with Swarek causes herself and Andy butt heads at first. Their different approaches to the job and to life in general contributes to their rocky relationship. But Marlo isn’t as straightforward as she seems—she’s got a secret, she's bipolar. When Andy finds out, Andy is sworn to secrecy as no one, not even Swarek knows. Marlo also has an unhealthy obsession with Kevin Ford after a predator case is closed, when she believes he is responsible. Andy and Swarek also get involved in this. After Marlo breaks into Ford's house and leaves her fingerprints, Andy has to lie in Marlo's records! When Kevin Ford constructs a hit-list with officers from 15 Division on it, he start beginning to pick them off. They rush to Marlo's house to check her safety, but Marlo left for her sisters. Then, in her basement, Nick Collins finds a study into Kevin Ford constructed by Marlo, including confidential records.
After an investigation into her, and how she can cope with being an officer and bipolar, she is given a job as a detective, for who Dov works for in season 6.