The Magician's Nephew

Jean Wildacre, a magician's assistant dies on stage after a trick goes wrong and she is stabbed with poisoned daggers. Barnaby and Jones's investigations lead them to the local Magic Circle, a group of people who once formed a cult together. Suspects include Ernest, Estelle, Isolde, Rosemary (Rosemary McHale) and Tristan Balliol; Aloysius and Simon Wilmington; Christine Turner and Hugo Cartwright.