Dr. Ralph Snyder and Dr. Frank Blake open an office together but soon split over a rivalry for nightclub singer Diana Wayne and a difference over ethics. In an effort to make some quick money and marry Diana, Blake becomes a retainer for gangster Joe Grant while the upright (and uptight) Sawyer becomes a medical examiner in the district attorney's office. Grant is involved in a murder and forces Blake to remove an identifying scar, thereby proving that all gangsters should keep a doctor on retainment. But Blake has a change of heart and shows up at Grant's trial, spills the beans and Grant is convicted. Consequently, Blake loses his license, Diana and then his life, proving that the "do-tell' doctor should have heeded the film title.