It follows the quest of Helena to find the relics of the cross on which Christ was crucified. Helena, a Christian, was the mother of the Roman emperor Constantine I.
The book has been described as lacking the characteristic biting satire for which Waugh is best known. However, the figure of Constantius Chlorus, Constantine's father, was interpreted by friends of the novelist as a caricature of Field-MarshalBernard Montgomery, a man Waugh mocked as a vainglorious social climber. More generally, the corruption and instability of the Roman society Waugh describes is reminiscent of the malaise and pragmatism that prevails over tradition and chivalric ethics at the end of the Sword of Honour trilogy. Helena's saintliness does not allow her to save her son from an imperial destiny she fears and disapproves of (at one point she fantasises about him becoming a provincial colonel); nor is she able to save her innocent grandson Crispus from being murdered on Constantine's orders in a palace struggle.