Contains spoilers for this episode and earlier episodes.
Gillian's boyfriend Dave Burns is abducted after meetings with a woman Lightman initially suspects is a lover. She is Michelle, Dave's former undercover partner, and his disappearance leads Cal into a drug organisation seeking revenge for its leader's death. The dead man's son, Little Moon, believes Dave killed his father. Cal offers to identify the killer and allows himself and Gillian to be taken to the place where Dave is being tortured.
Questioning reveals that Michelle became involved with Big Moon and was pregnant with his child. Dave is protecting another operative, but he refuses to name the person who fired the shot. Little Moon breaks his ribs and collapses his lung, forcing Cal to improvise treatment. Meanwhile, Torres and Reynolds question Michelle and use her memory of a previous beating to identify the location. Gillian is released, and agents close in.
Cal directs suspicion towards gang member Harris, provoking a confrontation in which Little Moon kills Harris for drawing a weapon on him. The FBI then arrests the gang. Dave privately admits that he killed Big Moon to protect Michelle's cover, and Cal acknowledges that he knew. Dave must be relocated, ending his relationship with Gillian. Emily also discovers an old paternity test in Cal's papers and challenges his distrust. Afterwards, Cal approaches Gillian as she sits alone at a restaurant.