At the Gull Point lighthouse, a woman lives all alone. Her strange story began years earlier with the rise to fortune and power of industrialist John Sinclair: Driven to a life of solitude by his distrust of his fellow man, Sinclair lives without love or companionship. One day, exhausted by his ruthless drive to attain wealth, Sinclair collapses and is ordered by his doctor to take a long rest. Deciding to take a cruise on the Great Lakes, Sinclair travels to Chicago and there collapses in a taxi driven by Ernie Sparrow. Sparrow, who is beloved for his kindness and consideration, takes Sinclair home and recalls a time when, as a famous boxer, he had no time for people or relationships. Sparrow declares that only by fleeing from fame and accepting the obscurity of life as a taxi driver did he find contentment and friendship. Sparrow insists that Sinclair, who has assumed the name John Carter, visit the local clinic, and there the doctor advises him to travel to New England for the healthful sea air. At the clinic, Sinclair meets nurse Joan Martin and her fiancé Fred Graham, a struggling intern. Believing that Sinclair has no money, Sparrow offers to buy him a ticket to New England, and out of gratitude, Sinclair invites Sparrow to accompany him at his expense. On the day of their departure, Sinclair reveals his true identity to Joan and proposes a business deal in which he will give her his entire fortune in return for her companionship during the few remaining months of his life. Weary of a life of poverty, Joan accepts his offer and asks Fred to wait for her. Unable to accept Joan's logic, Fred accuses her of being selfish and breaks off their relationship. In New England, Sinclair converts a lighthouse into a beach house, and as the months pass, he regains his health while Joan becomes lonely and restless and decides to leave him. Sinclair, who has fallen in love with Joan, offers to foresake the lighthouse and travel the world with her, and she agrees to give him another chance. Soon after, Fred visits the lighthouse and tells Joan that he has started his own practice and asks her to return to Chicago with him. Overhearing Joan reply that she needs time to make a decision, Sinclair invites Fred to stay with them. Sinclair, an accomplished chess player, describes a murder plot to Fred in which a murderer gets away with the crime by claiming that his victim fell out a window while sleepwalking. Fred takes Sinclair's bait, and decides to revise the plot to kill his rival. Feigning concern, Fred tells Sparrow about Sinclair's sleepwalking and asks him to buy locks for the windows. That night, Fred sneaks into Sinclair's bedrooom, planning to bludgeon him to death and then throw him from the window. Sinclair is waiting for Fred, however, and after knocking him unconscious, he drags his body to the window. Unable to open any of the windows, Sinclair carries Fred's body to the rocks where Sparrow sees him. When Sinclair explains that Fred fell out the window while sleepwalking, Sparrow replies that is impossible because he nailed all the windows shut. Sinclair then tells Sparrow the truth, and they return to the lighthouse and are greeted by Joan, who accuses Sinclair of murder and informs him that she has called the police. After Sinclair is electrocuted for his crime, Joan inherits his fortune. Haunted by tragedy, she is unable to escape her past and returns to the lighthouse to live out her life in desolation and torment.