Psychiatrist David Mercer is still reeling from the drowning death of his daughter Emma at their lakehouse a year ago. His marriage to Grace is crumbling under the weight of her blame and his guilt. When a drowned woman is found with David's business card, Detective Foster begins investigating a disturbing connection. Meanwhile, David's new patient Eliza Nash seems to know impossible details about his life-mentioning Grace by name and making cryptic references to the lakehouse. As more drowning victims appear with David's handwriting on notes dated in the future, the evidence points to an unthinkable conclusion: security footage reveals David conducting therapy sessions with an empty chair. Eliza Nash doesn't exist. Racing to the lakehouse where Grace has gone, David learns the truth from his mentor Dr. Webb-he's suffering a psychotic break. The drowned woman, Jane Reynolds, was a patient whose crisis call had distracted David the day Emma died. Consumed by guilt, Jane later drowned he