Tregaron's Daughter (1971)

These are some of the strange clues to the mystery that tormented a young English girl. In pursuit of them, her life changed dramatically and brought her from her father's fishing cottage to a agrand English manor. But the final clues to the mystery were in a distant palace in Venice and before her adventure was complete this fisherman's daughter would know to the full the terror lurking behind the ancient walls of that romantic city.