Suddenly the sky peels away like fabric and from the gaping hole fall two curious-looking children. Peter Schock and Kate Dyer have fallen straight from the twenty-first century, thanks to an experiment with an antigravity machine. Before Gideon and the children have a chance to gather their wits, the Tar Man takes off with the machine -- and Kate and Peter's only chance of getting home. Soon Gideon, Kate, and Peter are swept into a journey through eighteenth-century London and form a bond that, they hope, will stand strong in the face of unfathomable treachery.