The Sommerville Case

Private Investigator Harry Chadband flies his Piper Arrow to the French Riviera to keep tabs on the errant husband of a client, but ends up uncovering more than he bargained for. Although he's a brilliant detective, he doesn't seem able to pick up on the clues that both his client and his personal assistant view him with something more than affection. But of course there's the distraction of trying to prevent the annihilation of a major city.