After a doctor is found murdered, the chief suspect is a woman (Olivia De Havilland) identified by several witnesses at the scene. But the detective (Thomas Mitchell) assigned to the case discovers that she has an identical twin sister (also De Havilland) which begs the question ..... which one is the murderess? The director Robert Siodmak (THE SPIRAL STAIRCASE) and De Havilland tip their hand fairly early in the film so that we know who the murderer is so the suspense comes from how will they find out and will they find out before she commits another killing. Siodmak provides the requisite moody atmosphere and De Havilland does an excellent job of differentiating between the two sisters, it's really one of her best performances. Lew Ayres is the psychiatrist who attempts to find out which is the twisted sister through psychological means and ends up falling in love with one of them. The screenplay is by Nunnally Johnson who would return to the subject again nine years later with THREE FACES OF EVE. The effective underscore is by Dimitri Tiomkin. With Richard Long and Ida Moore.