A series of warehouse fires in the City of London attracts the attention of insurance investigator Quentin "Q" Barnaby, as well as that of attractive reporter Toby Collins and her photographer Jim Maxwell.
After yet another fire, in which a nightwatchman, trapped in the blazing building, is rescued by Barnaby and Maxwell, the investigator discovers the blaze was caused by an automatic teamaker containing hair lacquer that explodes when exposed to intense heat.