Insp. Crossley suspects an old woman of being responsible for an attack of food poisoning, but Kate soon discovers it was due to something entirely different - arsenic poisoning from old wall paper. Nick points out to Blaketon that the Insp. hasn't been keeping CID fully informed which soon puts an end to his presence in Ashfordly. The police are also surprised to discover that their new Inspector is a woman - Insp. Merchison!