A louse for the hangman

Mr Gorringer, headmaster of the highly-respected Queen's School, Newminster, disapproved of the publicity brought to his school by the extra-curricular activities of its amateur-detective history master, Carolus Deene. But when Lord Penge, a friend of long standing and a very rich one too, started to receive threatening letters, the headmaster decided to make an exception, and asked Carolus to investigate. The letters threatened death to Lord Penge, but it was Michael Ratchett, his secretary, who was found shot in the park of the Penges' luxurious house, Highearth Manor. Ratchett was found to be wearing Lord Penge's overcoat — had the murderer made a mistake and shot the wrong man?