A bedraggled street dog is about to perish in the cold winter night, after having been scalded by boiling water earlier in the day. Suddenly, an elegant man feeds him and takes him home. The dog's savior is a famous and wealthy medical professor who rejuvenates people by hormonal manipulations.

As soon as the dog becomes accustomed to his new life of plenty, he finds himself the subject of a strange experiment--the professor and his assistant implant the testicles and pituitary gland of a dead criminal into the dog's body. After a rocky post-operative course, the dog gradually begins to change into an animal in human form and names himself Poligraph Poligraphovich Sharik. The half-beast-half-man, who gets along very well in the prevailing proletarian society, turns his creator's life into a nightmare--until the professor manages to reverse the procedure.