Nancy receives an urgent message from her father Carson Drew, who is in River Heights, while she is touring in Europe with a group from Emerson College. She and her close friends Bess and George fly immediately to Venice, Italy. There, amid intrigue, the young detective begins her mysterious assignment involving an old Venetian family.
When the girls arrive, however, they are surprised to find their friends Ned, Dave, and Burt already on the scene--but in jail! The Emerson boys have been accused of stealing an invaluable collection of antique treasures.
Nancy must clear their names, despite the mounting evidence against them. Her efforts lead to exciting adventures as she journeys through a terrifying labyrinth of Venetian canals toward an unexpected discovery!