Donald Houston is George, an escapee from a French asylum (obviously Les Diaboliques had a big effect on Sangster, who also set Taste of Fear in France) who wants to kill his wife's lover. The wife is Nadia Gray, and the lover is Kerwin Matthews.
Donald Houston, a man escaping from a French asylum, seeks revenge against his wife's lover, Kerwin Matthews.  The wife, Nadia Gray, plays a central role in this plot.