Detective Mike Hoolihan (Patricia Clarkson) is investigating the murder of Jennifer Rockwell (Mamie Gummer), an astronomist at an observatory in New Orleans. She had presented a talk on black holes in the evening, but was found dead in the morning by the manager of the observatory (Toby James). She had been shot in the face, but there was no weapon. There is a sock and a jar of moisturizing cream found at the scene.
The manager claims that he was out all night with an associate. The sock is traced to Jennifer's boyfriend, who claims he left hurriedly to work on a new theory.
Jennifer's home is full of tchotchkes and other old nick-nacks. Mike passes out when she picks up a Florida snow globe, and imagines unique blue marbles similar to one that is on a string around her neck. When she comes to, she talks about the marble, and how she doesn't remember where it came from. She was an orphan, and has always had it.
Her co-investigator and supervisor suggest that this looks like "The .38 Caliber Killer", who killed young women, but hadn't struck in many years. The murderer always exchanged nick nacks with his victims.
While doing a more detailed search of the area, Mike finds a gun in a case, and a red scarf she had been having dreams about. The gun, a .38 revolver, is traced to the observatory manager, who admits he found it, and tried to dispose of it so he wouldn't be a suspect.
Figuring from where the gun originally lay, Mike concludes that Jennifer had shot herself. The investigators agree.
In photos of the crime scene, Mike realizes that there are no photos of the jar of moisturizing cream that she noted. When she buys a jar of the cream, she reacts as if memories come flooding back.
A video made during Jennifer's presentation on black holes shows some of the people who attended. There is a shadow of a man with a cap - very much like Jennifer's father's. Mike checks out the family home, and Jennifer's 2 brothers. She finds an old broach that Jennifer had been wearing, but was missing from the murder scene.
As she speaks with the family members, it becomes clear that Jennifer's father (James Caan) is an intimidating figure, and other family members are afraid of saying much around him. Mike notices that an object from one of the .38 Caliber Killings is in a picture of the family. A witness from one of the old murders recounts hearing the suspect walking as if he had a cane, just like Jennifer's father. In photos of the father, he seems to switch the cane from his right to his left hand, using it inconsistently.
It appears that the father had been killing young women who looked like his mother, but the killing had stopped when his daughter (Jennifer) was born.
Mike goes to a gun shop and buys a .38 revolver. She confronts Jennifer's father, but he grabs the gun from her and talks her out of her suspicions. She returns to the observatory, and considers suicide, but instead checks out an old, boarded up house.
In the house, she relives the murder of her mother. She was hiding in a closet when the .38 Caliber Killer shot her. Young Mike came out of the closet and rubbed the moisturizing cream on her dead mother's hands, asking her to wake up. Blue marbles had spilled all over the floor, and young Mike carries one out as she leaves with a police officer. The killer had taken the Florida snow globe.
Mike gets into her car, and drives away, know that she has solved the mystery of Jennifer's death, the .38 Caliber Killer, and her own demons.