The third instalment of the brilliant William Dougal series, from the bestselling author of The American Boy and The Ashes of London.

There's unfinished business between William Dougal and his widowed father. Part of it has to do with Celia Prentisse, William's ex-girlfriend. When her historian father is found drowned, it's declared suicide, but Celia remains unconvinced - not least because his abandoned clothes were found with a bottle of the wrong brand of gin and a slim volume of Schopenhauer's essays.

It's not much evidence, but it's enough to send her godfather, retired British intelligence officer Major Ted Dougal, and his son William off on a trail that leads to a 1930s arsenic poisoning and a still-classified World War I court martial . . .