In World War One, Martha Cnockhaert (Madeleine Carroll) works as a spy in a German hospital, acting for the allies. Aided by orderly Stephan (Herbert Marshall), Martha plots to blow up a German ammunition dump. When Martha accompanies a German Commandant to Brussels, a change in the Kaiser's movements inadvertently reveals Martha's true purpose.

1930s horror starring Boris Karloff as a scientist warped by the power he gains from one of his own discoveries. When Dr Laurience (Karloff) retires to an isolated house to research the origins of the human mind and soul with a surgeon, Clare (Anna Lee), and a man confined to a wheelchair, Clayton (Donald Calthrop), he is scorned by his scientific peers. However, Laurience succeeds in discovering a means of mind-transference: the ability to swap the mental faculties of any two people and thus to take possession of the bodies of others. But will he use the power wisely?