A secret, high-technology international agency called SHADO defends Earth from alien invaders.

Bertrand, an accountant employed by a large London firm, is called to the office of the Managing Director, Dreuther, to explain a mistake in the accounts. Dreuther is highly impressed by the young accountant's skilful explanation of the error and, hearing that Bertrand is soon to marry his spirited young fiancée, tells him to spend the honeymoon not in Bournemouth, but Monte Carlo at the company s expense! However, events in the fabulous Mediterranean paradise do not work out quite as Bertrand had envisaged...