Dr. Harvey Leith, deemed an inhuman murderer in the newspapers because three of his patients died after he tried an experimental serum, boards a freighter in Liverpool bound for the Canary Islands. Plagued by the memories of the surgery, Dr. Leith is weary and depressed and, when the ship's bar is closed to him, becomes annoyed and irritable. Suzan Tranter, who worked with Dr. Leith three years earlier during a diphtheria epidemic, is traveling with her brother Bobby to open a mission. When she attempts to console Dr. Leith, he remains aloof. After a few days of seclusion, the doctor meets Lady Mary Fielding, the wife of the richest rancher on Grand Canary Island, and they develop a friendship. He explains to her that enemies in his profession refused to allow him to use the serum until it was too late to save the patients; after the deaths, he says, the authorities swore that he used the serum without their knowledge. At Santa Cruz, Lady Fielding, realizing that she has fallen in love with Dr. Leith, decides that she cannot go back to her husband Michael after she sadly watches the doctor's ship leave the harbor to return to England. Dr. Leith, however, has been knocked out in a fight, and he awakens after the ship has departed. When he learns of a yellow fever epidemic, he goes to help with Suzan, who had jealously witnessed his interest in Lady Fielding. After Dr. Leith sets up operations at an old estate, Lady Fielding visits, but she arrives weak with the fever and collapses. Dr. Leith stays up with his unconscious love through many anxious nights and throws her husband out when he tries to take her home. After his serum takes effect on Lady Fielding, Dr. Leith finally goes to sleep, but he awakens to find that Suzan has allowed Fielding to take his wife away. After the disease is conquered in the native population, Suzan and Bobby, who earlier had fallen prey to the wiles of Lady Fielding's seductress friend, Elissa Baynham, open a welfare center. In England, Dr. Leith is honored by the medical society, and he receives a telegram from Lady Fielding that says she is happy for him.
