1666. London has been destroyed by fire and its citizens are looking for somebody, preferable foreign, to blame. Only the royal Court, with its strong Catholic sympathies, is trying to dampen down the post-conflaguration hysteria.

Then, inconveniently, a Frenchman admits to having started it together with an accomplice, whom he says he has subsequently killed. John Grey is tasked by Secretary of State, Lord Arlington, with proving conclusively that the self-confessed fire-raiser is lying. Though Grey agrees with Arlington that the Frenchman must be mad, he is increasingly perplexed at how much he knows.

And a body has been discovered that appears in every way to match the description of the dead accomplice. Grey's investigations take him and his companion, Lady Pole, into the dangerous and still smoking ruins of the old City. And somebody out there - somebody at the very centre of power in England - would prefer it if they didn't live long enough to conclude their work...