A young man's efforts to investigate his father's death and stop his mother from re-marrying land him in an insane asylum.

After his father, Judge Albert Cartwright, dies in a mysterious train accident, college student Paul Cartwright is haunted by nightmares in which a sinister stranger claims to be his new father. While on a fishing trip with Dr. Vincent, an old family friend, Paul receives a letter from his deceased father, telling him that it is now his responsibility to guard his young, naïve mother Virginia from unscrupulous men. Paul rushes home, where he learns that Virginia has begun seeing Brett Curtis, a businessman new to the area. Later, Paul faints after his young sister Dorothy shows him a new bracelet given to her by Brett, which looks just like the one she received in his nightmare. The next day, Paul goes through his father's legal files and notes the similarities between Brett and Claude Barrington, a murderer and child molester who has eluded prosecution. Paul's suspicions about Brett prove correct, as Brett is Barrington, and, having killed the judge, now plans to marry Virginia as a final act of revenge against the jurist. Worried about Paul's interference with his plans, Brett schemes to place the young man under the care of Professor Muhlbach, Brett's therapist and accomplice. Recognizing Brett and Muhlbach's alliance, Paul agrees to be treated by the psychiatrist at his sanitarium, in hopes of uncovering evidence against them, as well as delaying his mother's marriage. In the meantime, Brett convinces Virginia to break her promise to Paul and elope with him, knowing that Muhlbach plans to kill Paul once their nuptials are announced. Vincent arrives at the sanitarium just as Muhlbach is about to push Paul off the roof, and he and Paul then escape to an abandoned farm near the sanitarium, similar to the one in Paul's nightmare. There, they find pieces of the truck that was involved in the judge's train accident, which Vincent takes to Armstrong, the district attorney. A police investigation uncovers the rest of the truck, as well as fingerprints matching Brett's. Realizing that the police are on to them, Muhlbach orders Brett to meet with him at a golf course, but the molester is diverted by his attraction for Dorothy. Meanwhile, Paul learns that Brett and Dorothy have gone alone to the family's summer cottage, so he races there with his friends, George and Lydia. They arrive just in time to save Dorothy from Brett's lecherous advances. Brett knocks Paul unconscious and grabs a knife off the boathouse's wall, but then is shot and killed by the police before he can inflict any further damage. In turn, Muhlbach is captured by the police, ending Paul's nightmares for good.