There is both excitement and dismay in Llanfair when a new French restaurant opens. The glamorous owner, Madame Yvette, tries to win over the locals, and everything seems to be going well until a string of fires plagues the town. One night the restaurant burns down, and a body is found in the rubble.

Constable Evans joins Sergeant Watkins to follow a trail of clues that leads them to the South of England and then to France, and finally to the conclusion that a dangerous killer is loose in Llanfair.