A Puzzle of Poppies - Sherwood & Jarvis, #1

He expected magic. What he got was murder.   Following a disastrous stint in Her Majesty's army, Dr. Wilfred "Wilf" Jarvis finds himself jaded and directionless. Hoping for a fresh start, and perhaps a bit of the storybook magic he'd yearned for as a boy, he accepts a diplomatic posting among the Fair Folk of the Seelie Court. When he arrives, however, he is drawn into a web of political machinations and bitter grievances that prove just as disappointing as his other pursuits - until the body of a British soldier is discovered in Folk territory. Before he realizes exactly what's happened, he's enlisted by Honoria Sherwood, a brilliant half-Folk, half-human polymath, in a worryingly high-stakes murder investigation.
With tensions mounting between the Folk and the British Empire, the two must track down the killer or lose their only chance to see true justice done.