Inspector Sam Blackstone has dealt with arsonists before — but never one quite like this.

If the arsonist’s true purpose is to make the government hand over one hundred thousand pounds, why does he seem so reluctant to apply the necessary pressure?

Why does he content himself with burning down a single warehouse, when he could set an entire riverside wharf ablaze? And why firebomb a single sloop, when it would have been just as easy to destroy the whole fleet?

In order to answer these questions, Blackstone—aided by Dr Ellie Carr, a passionate disciple of the new science of criminal pathology—must follow a trail of death and destruction.

That trail will lead them to the very centre of government itself. And, not for the first time, Blackstone soon realises that in solving this case, he may well be destroying his own career.