The book returns Dick and Dorothea Callum, known as the Ds, to the Norfolk Broads where they renew their friendship with the members of the Coot Club.

This book is more of a detective story as the Ds and Coot Club try to unravel a mystery that threatens the Death and Glories' freedom to sail the river.

Unfortunately, they find the Death and Glories (Pete, Bill and Joe) coming under a gathering cloud of suspicion of setting moored boats adrift.

Eventually, with the help of the owner of the Cachalot, a carefully prepared trap is sprung and in a flash (literally, to take a night photo of the real culprits) the villains are discovered and the boys are exonerated.

The penitent constable Tedder makes a humble and heart-felt apology to the children for having naively believed the word of the culprits over their own protests of innocence, and promises to never distrust them again.