The action occurs twelve years later on from the last novel, when Hannay, now in his fifties, is called by an old oath to protect the son of a man he once knew, who is also heir to the secret of a great treasure.
The narrative takes place twelve years after the prior book, with Hannay, now in his fifties, being called upon by an old commitment to protect the son of someone he previously met, who is also inheriting the secrets of a significant treasure.