In the short story The Chocolate Box, John Wilson is an English friend of Paul Déroulard. He had come to Brussels from England on some business and had asked Déroulard to put him up. Wilson suffered from angina and had a prescription for trinitrine. He had had such a prescription filled from an English chemist in Brussels. While investigating the death of Paul Déroulard, Poirot's wondered why Wilson would have come to Brussels without having brought enough trinitrine with him. He speculated that he might have lost a bottle of it. Félice, the chambermaid in charge of Wilson's room confirmed that Wilson had indeed lost a bottle of trinitrine. Poirot then surmised that the killer might have taken it to poison Déroulard. Trinitrine was made to taste like chocolate and so could be introduced into the chocolates which Déroulard ate.