At the Geste family home in Devon, the family heirloom, the Blue Water sapphire, mysteriously disappears. And there is a recounting of a curious tale from the Sahara desert.

Lady Brandon has had a mysterious Indian visitor while Beau is hiding in a suit of armour, and John in a chest. When the visitor leaves, John is taken from his airless hiding-place, apparently lifeless.

The Blue Water has been stolen, and no one will confess to the theft. Now Beau has disappeared.