Summer 1914. A London-based private detective, Sergeant Dagger, is employed by Celia Harrison, a suffragette, to discover why her husband, an army Captain, has committed suicide.Unconvinced by the official verdict of melancholia, Celia wants the truth - as do MI5, who also recruit Dagger. As WW1 breaks out, Dagger reluctantly joins the British Expeditionary Force, and sails to France with the first battalions.There he uncovers a web of deceit and hypocrisy lying at the heart of the British Army. Operating along the fast-moving front-line, Dagger sees the death of the first British soldier, flies with the Royal Flying Corp into occupied Belgium and fights at the Battles of Le Cateau and the Aisne. Later, reassigned to libertine Paris, Dagger, an amateur artist and poet, meets modernist icons Picasso, Cocteau and Apollinaire before discovering the identity of a mysterious painter called Fevert and helping MI5 solve one last problem.