Impossible Secret of Lillian Velvet

Welcome to the world of Lillian Velvet: a very proper girl named Lillian Velvet is living a very lonely life with a nasty grandmother; she's given a jar of coins, each with the power to take Lillian on a journey to a different time and place...and also to grant a single wish. She comes across a small boy in a barn about to be crushed to death by a load of hay; a family, each member in mortal danger, who are strangers to Lillian (but whom clever readers will recognise...). And a web of dangerous magic is closing tight around all. Who IS this Lillian Velvet? And what on earth is her secret?