Shock.

Dr. Cross (Vincent Price) is treating a young woman, Janet Stewart (Anabel Shaw) who is in a coma-state, brought on when she heard loud arguing, went to her window and saw a man strike his wife with a candlestick and kill her. He then takes her to his sanitarium and at Elaine's urging, gives Janet an overdose of insulin under the pretense of administering insulin shock therapy. He can't bring himself to murder her in cold blood, though, and asks Elaine to get the medicine to save her. Elaine refuses, they argue, and he strangles her.