Three days after he disappeared on his way to see 'Don Giovanni' at Covent Garden, food critic Robin Skelton is found wandering in the Mexican desert. The Department is called in to investigate, and it becomes apparent that Skelton was mistaken for his double, rocket scientist Peter Sinclair, who is involved in tests for the American space schedule. Once they realize this, they discover that in the meantime Sinclair has also been kidnapped. The only clue Skelton can give the Department is 'Turtle in the Shell', which leads them to the Bahamas, where Sinclair has been taken by villainous Dr. Wolf.
—don @ minifie-1