When a phantom horseman-headless, of course-appears amidst the rhododendron at England’s Calladale College of Agriculture for women, the incident is passed off as a rag pulled by the rival men’s college, Highpepper Hall. But when the badly decayed body of a young woman- a Calladale student, to judge from the badge on her jacket-is discovered in an abandoned coach, it becomes obvious that something much more sinister then a prank has been played. Dame Beatrice Lestrange Bradley, psychiatrist and consulting psychologist to the home office, whose pig farming nephew, Carey holds a temporary position at the college, is called in to investigate.

Dame Beatrice’s first deduction is that the murderer-for this was no accidental death-must have possessed a particular knowledge of poisonous plants in order to choose spotted hemlock, which was at its most deadly at that time of year. Her second conclusion is that the murder victim is not at all who she was originally though to be…