February 2014: Police Capitaine Inés Picaut is called out to investigate a blaze in the old town of Orléans. This is the fourth in a series of increasingly brutal arson attacks, and at the centre of the conflagration lies a body. An Islamic extremist faction claims responsibility, but Inés and her team cannot trace its whereabouts, or any evidence of its existence. And a partly melted memory card found in the victim's throat is the only clue to his identity.

September 1429: Joan of Arc is in the process of turning the tide of The Hundred Years' War. English troops have Orléans under siege, and Tomas Rustbeard, the Duke of Bedford's most accomplished agent, finally has her in his sights. But he knows that killing 'The Maid' – the apparently illiterate peasant girl who nonetheless has an unmatched sense of military strategy and can ride a warhorse in battle – is not enough. He must destroy the legend that has already grown around her. And to do that, he must get close enough to discover who she really is.

More fires rage and the death toll mounts while Inés fights to discover what connects an expert in the analysis of war graves, the unquenchable ambitions of the Family which seeks to hold the city in its absolute power, and the discredited historical theories of her own late and much lamented father.

When Tomas risks everything to infiltrate the hotly defended inner circle of the Saviour of France, he finally discovers a secret that will prove as explosive nearly six hundred years later as it would do if revealed in his own time.