Sir Borotyn, a prominent Prague resident, is discovered murdered in his home, with all indications pointing to a vampire assault. The victim's friend, Baron Otto, and the physician who analyzes the body, are certain that the vampire is the mysterious Count Mora or his daughter. Receiving little help from the law, Professor Zelen, an expert in the occult, is called in to assist with their investigation.

Lionel Barrymore
as Professor Zelin

Elizabeth Allan
as Irena Borotyn

Bela Lugosi
as Count Mora

Lionel Atwill
as Inspector Neumann

Jean Hersholt
as Baron Otto

Henry Wadsworth
as Fedor Vincente

Donald Meek
as Dr. Doskil

Jessie Ralph
as Midwife

Ivan F. Simpson
as Jan

Franklyn Ardell
as Chauffeur