Sartorius (Karloff) is a doctor whose research into paralysis has left him penniless. He meets Lady Yvonne Clifford (Goya), the wife of elderly cotton tycoon Sir Charles Clifford (Selten). She wants her husband's money and Sartorius agrees to kill the old man in exchange for half his
estate. Hired as the family physician, Sartorius gives Sir Charles a series of injections that slowly poison him. Sir Charles suspects what is happening and transfers his estate to Roger (Margetson), his son from a previous marriage. Lady Yvonne learns of the switch and she demands Sartorius kill
both her husband and his son. However, Sartorius' nurse, Eve (Wyndham), who is in love wit...