Flashpoint — John Russell Fearn

Gordon Drew's return to his home town coincides with a baffling series of fires and murders. Drew finds himself secretary to a Dr. Carruthers, an eccentric scientist and investigator, who helps the police solve the mystery of the fires. Meanwhile, Superintendent Denning's methodical investigations lead him to the arsonist. However, when he also discovers a ruthless murderer who exploits science to dazzling effect in his crimes, it is Dr. Carruthers who excels and helps Denning bring justice to the criminal.