One Way Out — John Russell Fearn

On a train trip to Scotland with his chief clerk Martin Lee, London financier Morgan Dale is suddenly confronted by his embittered ex-Secretary, whom he's recently sacked. Janice Elton had once been obsessed with him, but the happily married Dale had spurned her romantic advances. Now, Janice wants her revenge. Returning to their carriage, Lee finds Dale alone with the dead body of Janice, whom Dale claims has committed suicide by taking strychnine. With the situation incriminating Dale, Lee advises him to remove any identification and throw the girl's body from the train. But when the police eventually identify her and come to believe she's been murdered, Lee begins to blackmail Dale. And then there's only One Way Out....