Madam, Will You Talk? Mary Stewart

Widowed Charity Selborne had been greatly looking forward to her driving holiday through France with her old friend Louise - long, leisurely days under the hot sun, enjoying the beauty of the parched Provencal landscape. But when Charity arrived at their hotel in the picturesque French town of Avignon, she had no way of knowing that she was to become the principal player in the last act of a strange and brutal tragedy. Most of it had already been played. There had been love--and lust--and revenge and fear and murder.

Very soon her dreams turn into a nightmare, when by befriending a terrified boy and catching the attention of his enigmatic, possibly murderous father, Charity has inadvertently placed herself center stage. She becomes enmeshed in the schemes of a gang of murderers. And now the killer, with blood enough on his hands, is waiting in the wings.