London, 1918 Fiona Figg finds herself back in Old Blighty saddled with shuffling papers for the war office. Then a mysterious card arrives, inviting her to a fancy house party at Mentmore Castle. This year's Ascot-themed do will play host to a stable of animal defense advocates, and Fiona is tasked with infiltrating the activists and uncovering possible anti-war activity. Disguised as the Lady Tabitha Kenworthy, Fiona is more than ready for the "mane" event, but the odds are against her when both her arch nemesis, dark-horse Fredrick Fredricks, and would-be fiancé Lieutenant Archie Somersby arrive unexpectedly and "stirrup" her plans. And when a horse doctor thuds to the floor in the next guest room, Fiona finds herself investigating a mysterious poisoning with some very hairy clues. Can Fiona overcome the hurdles and solve both cases, or will she be put out to pasture by the killer?