Chartered accountant Harold Eastwood, conventionally minded, chances to meet Alec Goodrich on the train, travelling first-class with a third-class ticket.

Alec is a best-selling novelist. He soon finds Harold's knowledge of income tax allowances useful and when Alec pays a visit to the accountant his wife, Isabel, who yearns for culture and literature, quickly takes up the fantasy to be his mistress. However, not she but Irma, the Austrian barmaid at the tavern, has caught Alec's wayward fancy...