Postcards from a Stranger — Sally Stewart

Returning home to Little Fairford, Oiver Hatton finds Jane Kingsley, who he remembers as a gauche, unhappy teenager, astonishingly transformed into a confidant young woman.
Her uncle's valuable collection of antique scientific instruments attracts expert study, while Jane herself attracts visiting researcher Jules Legrand. But after a burglary and the death of Jane's uncle, Oliver Hatton distrusts them both - particularly when they disappear and the instruments left behind are found to be fakes.
Torn between old and new loyalties, Jane goes in search of Jules and the missing collection, following clues that lead her across France. With Oliver at her heels , the trail leads to danger and confusion - who to trust, who to love . . . ?