Biggles is on a cruise after being advised by his doctor that he needs a rest. Algy and Ginger are travelling with him. To their surprise, the ship is attacked and sunk off the coast of Spain. Biggles, Algy and Ginger swim to the shore and find themselves in Barcelona. Going for a drink in a bar-restaurant called 'Casa Reposada' turns out to be a big mistake. Our heroes are plunged into espionage when a man called Fraser, who Biggles once met, gives him a coded document that must be taken to the British Foreign Office.