Westerson, Jeri. Crispin Guest novels.

""Creative and enthralling. If you enjoy authentic Medieval history combined with modern suspense, this one's for you." --John Lescroart Once a Knight of the Realm, Crispin Guest was stripped of his title and his lands and must now earn his meager living through his wits. With the help of his young apprentice, reformed thief Jack Tucker, Guest is known to certain populations as The Tracker, the man who can find anything--for a price. It is for that reason that Guest is sought out by Nicholas Flamel, an absent-minded 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. Then Flamel's assistant turns up--dead, hanging from the rafters with a note pinned to his chest by 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. Guest must rescue the missing wife and find the stone before it falls into unworthy hands"--

"Once a Knight of the Realm, Crispin Guest was stripped of his title and his lands and must now earn his meager living through his wits. With the help of his young apprentice, reformed thief Jack Tucker, Guest is known to certain populations as The Tracker, the man who can find anything--for a price. It is for that reason that Guest is sought out by Nicholas Flamel, an absent-minded 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. Then Flamel's assistant turns up--dead, hanging from the rafters with a note pinned to his chest by 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. Guest must rescue the missing wife and find the stone before it falls into unworthy hands"--