The Time Travelers (The Gideon Trilogy, Book One)

Gideon Seymour, thief and gentleman, hides from the villainous Tar Man. 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 Peter and Kate's only chance of getting home. Soon Gideon, Peter, and Kate 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.