Blackmail is a detective story set in 1916 in Paris and the Western Front during the First World War. Agents from Germany, France and Great Britain are engaged in a web of blackmail that Captain Jamie Brown has to unravel in case the "Big Push" (the Somme offensive) is compromised and a royal sex scandal exposed.
Jamie finds himself on a personal journey that questions his beliefs and his ability to control his nerves and his drinking as he wrestles with his own country's deep state, a fractious ally, and an enemy master-spy.
The action ranges from the frontline trenches to the brothels of Paris, and along the way Jamie meets snipers, fighter aces, spies, gangsters, prostitutes, and establishment figures, as he tries to identify who is ultimately behind the inter-twined strands of blackmail.
The plot is set against real military and political events of the time. It explores Edwardian social mores including rumours about the members of the Royal family. The novel also deals with recognisable modern themes of gay rights, fake news, kompromat, injudicial killing, and organised crime in a war-time context. Finally the Scottish etymology of the word "blackmail", and its fittingness for this case, is unveiled at the end.