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Leaving behind his wife, Carol (Valerie Hobson), writer John North (Richard Todd) goes on a train trip with his mistress, Susan Wilding (Christine Norden), whose husband publishes North's books. En route, thinking they're being tailed, John pulls a cord that triggers an emergency stop, then jumps off the train. He later learns that the train crashed after his exit, apparently killing Susan. But, when they discover that Susan was shot before the crash, investigators close in on North. Wikipedia