The Danish Ambassador has requested Albert Campion's help on 'a delicate family matter'. He's very concerned about his eighteen-year-old daughter, who has formed an attachment to a most unsuitable young man. Recruiting his unemployed actor son, Rupert, to keep an eye on Frank Tate, the young man in question, Mr Campion notes some decidedly odd behaviour on the part of the up-and-coming photographer. Before he can act on the matter, however, both the Ambassador's daughter and her beau disappear without trace. Then a body is discovered in a lagoon.