I was just going through the old Bad Machinery looking for something else, and I think I figured out what you weren’t quite remembering. In “The Case of the Good Boy”, which was the one before “Simple Soul” where Claire’s arsonist streak came out, there was a kid named Benny Marks who’d been bullying Jack. At the end of the case, Ryan busted him for it, after Jessica’s friend Sian informed on him, and it came out that Benny was also responsible for the cricket pavilion burning down, because he hadn’t put out his cigarette before tossing it when Ryan and Miss Perks had busted him for smoking earlier in the case.