In fourteenth century London, Crispin Guest is a disgraced knight convicted of treason and stripped of everything that matters to him: his land, title and honor. With only his wits with which to survive, Guest has become known as the "Tracker" - a man who can find anything, can solve any puzzle and, with the help of his apprentice, Jack Tucker, an orphaned street urchin with a thief's touch --will do so for a price. But this time, even Crispin is wary of taking on his most recent client. Jacob of Provencal is a Jewish physician at the King's court, even though all Jews were expelled from England nearly a century before. Jacob wants Crispin to find stolen parchments that might be behind the recent, ongoing, gruesome murders of young boys, parchments that someone might have used to bring forth a demon which now stalks the streets and alleys of London.