Turn Coat by Jim Butcher

The search for a traitor in the highest circles of power forms the main plot thread of Butcher's 11th hard-boiled fantasy novel featuring Chicago's wizard detective Harry Dresden (last seen in 2008's Small Favor). Harry, a warden of the magic-governing White Council, finds himself in an unusual position when Morgan, his fellow warden and frequent antagonist, asks for his help. One of the White Council's leaders has been murdered, and Morgan was found at the scene of the crime holding the murder weapon. If he has been framed, then another senior wizard is behind the killing and may be trying to destroy the council entirely. Aided by werewolf and vampire allies, Dresden investigates with his trademark sardonic noir flair. Despite the sprawling plot, both fans and newcomers will get into the fast-paced action.
Butcher’s series star, wizard detective Harry Dresden, has been facing ever more varied and dangerous trials. Once just Chicago’s only wizard PI, Harry is now a warden of the White Council of Wizards—that is, one of the enforcers of its rules—and it seems as though every time he gets a better grasp on his magical strength, his enemies worsen. When the “parole officer” of Harry’s youth, Morgan, grievously injured and pursued by the wardens, comes to Harry for help, it’s the opening salvo of serious confrontation with the council. Morgan stands accused of killing senior council member LaFortier. The murder was certainly an inside job, and time is short to find the real killer before Morgan is summarily executed. Simultaneously, something unbelievably horrible and by all accounts far too powerful to take on alone is stalking Dresden. Searching for the killer, Harry’s caught up in a plot leading to the White Court vampires and the very halls of the White Council. Meanwhile, his dog’s daily duty is keeping Harry’s apprentice and Morgan from one another’s throats. Fortunately, Harry’s sense of humor lightens the tone of even the most serious confrontation, so though Butcher has turned up the tension here, this is an amusing, satisfying, and action-packed addition to the Dresden Files.