Furious at being jilted at the altar by Margaret Langton, Charles Moray left England behind him. Four years later, he returns only to discover that a criminal gang has been using his house to plan a vicious crime. The target is the beautiful Margot Standing, who stands to inherit a considerable fortune. But the gang has other plans for her.
Charles is appalled to discover that Margaret Langton is one of the conspirators. How did she come to be involved? And who is the terrifying masked man who has her in his thrall? Charles turns to Miss Silver to uncover the strange truth behind Margaret's complicity, and the identity of the terrifying and mysterious individual behind the grey mask.
Miss Silver, a retired governess-turned private detective, often compared to Miss Marple, works closely with Scotland Yard, especially Inspector Frank Abbott and is fond of quoting the poet Tennyson.