Book of Midnights

In the mid 1930's, two powerful sorcerers, Katie McMath and Roger March, are recruited by a US Senator to undertake a secret mission to recover the fabled Book of Midnights, supposedly a tome that contains sorcery secrets that will make the owner extremely powerful, but unprepared for the truth about that book, Katie finds herself proceeding alone, gamely trying to do what's right despite mounting opposition, but she discovers an unexpected ally.