Nahendra Nao, heir to the Maharajah of Chitipur, unwisely lets Elsie Marsh of the Casino de Paris wear his priceless ancestral pearls, which react badly to her skin.

To provide cover, Lydia is to act as paid companion to a woman introduced by Carruthers, Lucrece Bouchette; while Oliver Ransom, an ex-Captain of the Bengal Police, is added to the party to protect the pearls.

He senses an uneasy atmosphere, and is on his guard when Guy Stallard, an American millionaire, invites him and the houseboat party to a fancy dress ball at a large house he has rented nearby.

But things go awry – resulting in Lydia being kidnapped and Ransom murdered – when Carruthers' co-conspirators refuse to act as his chessmen, taking their orders instead (as Hanaud points out) "from their lusts and hates".

He particularly praised the "clever and impelling study of conflicting characters built around the striking and original idea of the perfect crime ... going all awry simply because the people concerned were ordinary human beings".