Trouble With Product X // Beware of the Bouquet — Joan Aiken

In The Shadow. It had begun like a routine, uneventful assignment -- accompanying the agency film crew on location in Cornwall. It might, Martha Gilroy hoped, even help her forget Lucian, the man she had loved and lost. But high on the rocky Cornwall cliffs, in the shadow of a silent and eerie castle, Martha discovered that a madman was stalking her -- a phantom who believed she had something he needed. Martha fled in terror to the castle for sanctuary -- but there, hiding in the shadow, Lucian waited.