Loser Takes All by Graham Greene

Bertram had no belief in luck. He was not superstitious. A conspicuously unsuccessful assistant accountant, he was planning to get married for the second time. Quite quietly: St Luke's, Maida Hill, and then two weeks in Bournemouth. But Dreuther, a director of Bertram's firm, whimsically switches wedding and honeymoon to Monte Carlo. Inevitably Bertram visits the Casino. Inevitably he loses. Then suddenly his system starts working . . .