Dark Fire is set in the summer of 1540, a few years after Henry VIII es­tab­lished himself as the head of the Church of England. Matthew Shardlake is a London lawyer, who takes on a case defending a young woman against the charge of murdering her 12-year-old cousin. She refuses to speak and will be "pressed" by heavy weights until she enters a plea—or dies. In exchange for a temporary reprieve, Shardlake agrees to take on an in­ves­ti­ga­tion for his sometime patron, Thomas Cromwell, Henry’s first minister. An alchemist claims to have discovered the secret of Greek fire, a terrible napalm-like weapon once used in the Byzantine empire. Shardlake has twelve days to find the cache of dark fire.

Sansom recreates Re­for­ma­tion London, seamlessly blending together a stew of religion, politics, and skull­dug­gery, in a very en­ter­tain­ing mix.