Once a Knight of the Realm, Crispin Guest was stripped of his title and his lands and now must earn his living with his wits. In various corners of late fourteenth-century London, Guest has become known as the Tracker, a man who can solve any puzzle or find any missing object - for a price. Because of that reputation, Guest is sought out by Nicholas Flamel, a famed alchemist. Both Flamel's wife and his apprentice are missing, and he wants Guest to find them and bring them home.

Before he can even begin looking, Guest discovers that Flamel's house has been ransacked. Ancient symbols start appearing on walls and carved into stones around London, and Flamel's assistant turns up dead, hanging from the rafters with a note pinned to his chest with a dagger. It is a ransom note that promises the safe return of his wife in exchange for the Philosopher's Stone, which is reputed to turn lead into gold and create the Elixir of Life. And the kidnappers aren't the only ones after it. From the highest nobility to Flamel's fellow alchemists, everyone is seeking the Stone for themselves. With the help of his young apprentice, former cutpurse Jack Tucker, Guest must use all his skills and wits to unravel the mystery, rescue Flamel's kidnapped wife, and find the Stone before it falls into unworthy hands.