Someone is targeting the city's magic practitioners, the members of the supernatural underclass who don't possess enough power to become full-fledged wizards. Many have vanished. Others appear to be victims of suicide. But the murderer has left a calling card at one of the crime scenes--a message for Harry Dresden, referencing the book of Exodus and the killing of witches.
Harry sets out to find the killer before he can strike again, but his investigation turns up evidence pointing to the one suspect he cannot possibly believe guilty: his half brother, Thomas. Determined to bring the real murderer to justice and clear his brother's name, Harry attracts the attention of the White Court of vampires, becoming embroiled in a power struggle that renders him outnumbered, outclassed, and dangerously susceptible to temptation.
Harry knows that if he screws this one up, a lot of people will die--and one of them will be his brother.
A year after the events in Proven Guilty, Dresden is called by Murphy to the scene of an apparent suicide, and senses the victim is a magical practitioner. After investigating another victim, Dresden realizes a serial killer of magical practitioners is loose in Chicago. Investigating, he meets with a group of practitioners who've banded together and hired Elaine, Harry Dresden's former lover, for protection. He finds that his brother had apparently been following most of the women who've vanished, but also comes across another suspect, "Grey Cloak," whom he tracks to Undertown, a warren under Chicago, and spies on him meeting with Cowl—who didn’t die during the Darkhallow (in Dead Beat), also learning that vampires of House Skavis — who feed on despair — are responsible for the suicides. Cowl detects Dresden and blasts his psychic thread. Dresden wakes up next to his melted model of Chicago, which absorbed most of the blast.
After incorrectly singling out a practitioner, Helen, as an accomplice, Dresden tracks Thomas to his boat, where they learn that Thomas has been smuggling magically talented women out of the city to protect them. Before Thomas can finish explaining, Madrigal Raith and his ghouls attack, and the group flees. Following more deaths and investigation, Dresden figures out the Skavis is one of the women in time to save Elaine from its attack. Elaine is hospitalized, so Dresden calls Carlos Ramirez to help him fight Grey Cloak and Madrigal.
Dresden, Ramirez, Molly and Mouse head to the Raith estate for the White Court conclave. Lara Raith escorts Dresden and Ramirez into the Deeps, a cavern, where they wait until the right moment to challenge Vittorio "Grey Cloak" Malvora and Madrigal to combat for violation of the Unseelie Accords. Vittorio and Madrigal accept the duel to the death. They all fight with a combination of physical and magical weaponry and defenses. Dresden kills Madrigal. Vittorio calls Cowl, who opens a gate from Nevernever, ushering in an army of ghouls. While the ghouls rampage, Dresden opens another gate. Thomas, Murphy, Marcone, and his mercenaries arrive with automatic weapons and high explosives. They escort Lord Raith, Lara, and their entourage to Dresden's gate. Vittorio casts a spell that crushes Dresden, Lara, Thomas, and Marcone to the floor. Inside a time warp bubble, Dresden and Lash, the demonic shadow possessing Dresden, discuss free will and Lasciel's coin. Dresden refuses to accept the coin to defeat the vampires. Tortured by self-awareness, Lash sacrifices herself to protect Dresden's mind from Vittorio's spell. Suddenly free, Dresden blasts Vittorio with Marcone's shotgun, breaking the spell on the others. As Thomas hauls Marcone through the gate, Cowl closes it, stranding Lara and Dresden. Marcone's explosives go off and the cavern collapses. Dresden folds his shield into a bubble around Lara and himself. They ride the explosion of fire out of the tunnel to safety.
Dresden finds out Lara was behind the plot to kill the female practitioners, and extracts a restitution and bond against future killings. Discussing the future with Elaine, he encourages her plan to develop and spread a safety net for practitioners. In exchange for his help, Marcone becomes a freeholding baron under the Unseelie Accords. Later, Dresden digs up Lasciel's coin and gives it to Father Forthill.