Detective Mike Hoolihan (Patricia Clarkson) embarks on a complex investigation following the shocking murder of Jennifer Rockwell (Mamie Gummer), an astrophysicist who was found dead at an observatory in New Orleans. Just hours earlier, Jennifer had captivated her audience with a talk on black holes, only to be discovered lifeless the next morning by the observatory’s manager, Prof Ian Strammi (Toby Jones). Mysteriously, Jennifer was shot in the face, yet there was no firearm present at the scene. Odd objects such as a sock and a jar of moisturizing cream become significant clues as the investigation unfolds.
Initially, the manager claims an alibi, stating he was out throughout the night with an associate. However, the sock leads back to Jennifer's boyfriend, who insists that he left in haste to work on a groundbreaking theory. As Mike delves deeper, she finds Jennifer's home cluttered with forgotten treasures and quirky souvenirs. While inspecting a Florida snow globe, Mike faints, and upon regaining consciousness, she reflects on a unique blue marble that hangs around her neck—an artifact tied to her childhood as an orphan.
Throughout the investigation, Mike and her colleague consider the chilling possibility that this murder connects to an old case involving "The .38 Caliber Killer," a notorious murderer of young women, who would exchange trinkets with his victims. While surveying the crime scene, Mike uncovers a hidden gun and a red scarf from Jennifer's dreams. Tracing the .38 revolver back to the observatory manager, he admits to having discovered it and attempting to hide it to avoid suspicion. The team reaches a consensus that Jennifer may have taken her own life.
However, as Mike revisits the crime scene photos, she realizes a crucial clue is missing: the jar of moisturizing cream. Purchasing a similar jar triggers a flood of memories for her. A haunting video of Jennifer's black holes presentation captures a shadowy figure resembling Jennifer’s father, Colonel Tom Rockwell (James Caan). Intrigued, Mike speaks with Jennifer’s two brothers and discovers an old brooch previously worn by Jennifer but absent from the crime scene.
As Mike uncovers more details about the family dynamics, she learns that Colonel Rockwell commands an air of intimidation, making others wary of him. A witness from the past murders describes the killer’s distinctive gait, reminiscent of walking with a cane—an accessory that Colonel Rockwell is seen using inconsistently in photographs. This points to a disturbing possible motive, suggesting he may have been targeting women who resembled his own mother.
Convinced of a connection between the past and present, Mike buys a .38 revolver at a gun shop and confronts Colonel Rockwell, but he manages to disarm her both literally and figuratively, dissuading her suspicions. In a state of turmoil, she contemplates suicide at the observatory but instead decides to explore an abandoned house filled with painful memories.
In this house, Mike is transported back to a time when she witnessed her mother's murder firsthand, recalling the moment she emerged from a closet and smeared moisturizing cream on her mother’s lifeless hands, pleading for her to awaken. Scattered around were blue marbles—remnants of her childhood, and one of these she carries away as she departs with a police officer. The notorious Florida snow globe was also taken by the killer that night.
As she drives away from the haunting memories, Mike realizes she has unraveled not only the mystery behind Jennifer's tragic death but also confronts the historical terror of the .38 Caliber Killer and her own buried traumas.
