Long ago, Susan Rodriguez was Harry Dresden's lover-until she was attacked by his enemies, leaving her torn between her own humanity and the bloodlust of the vampiric Red Court. Susan then disappeared to South America, where she could fight both her savage gift and those who cursed her with it.
Now Arianna Ortega, Duchess of the Red Court, has discovered a secret Susan has long kept, and she plans to use it-against Harry. To prevail this time, he may have no choice but to embrace the raging fury of his own untapped dark power. Because Harry's not fighting to save the world...
He's fighting to save his child.
With a phone call, Susan Rodriguez informs Harry Dresden that they have a daughter, Margaret Angelica, who has been kidnapped by Duchess Arianna, the widow of a Red Court duke that Ebenezar McCoy killed several years earlier. Dresden goes to Edinburgh to seek help from the Council. However, upon his arrival, he discovers Arianna is there, hosting a peace conference with the rest of the Council. Dresden openly challenges Arianna to a duel to the death over his daughter's kidnapping, but is prevented from carrying it through by the other members of the Council. Infuriated, Dresden returns home.
After an explosion destroys his office building, Dresden learns from Karrin Murphy he is under investigation by the FBI. After being released and having a talk with his fairy godmother, Dresden is eventually directed to the Norse God Odin, who tells him The Red Court is going to use Margaret for a powerful blood curse that will kill everyone who shares a relation to Maggie, including Dresden. Dresden decides to investigate Rudolph, the FBI agent who implicated him in the office explosion, reasoning that he must have implicated Dresden because of pressure coming from the Red Court. During this investigation, he encounters the 'Eebs', a husband and wife team of Red Court vampires who have been sent to both assassinate Rudolph and to dissuade Dresden from going after Arianna. After a close call with them, Dresden returns home, only to have his apartment firebombed. During his subsequent attempts to rescue the other residents in his building, Dresden's back is broken, and Sanya shows up just in the nick of time. While injured, Dresden calls up Uriel and asks for help. Uriel, in the form of a tall young man in jeans and a T-shirt, refuses to heal his back as it would alter the consequences of Dresden's choices made in free will. With no other options open to him, Harry turns to Queen Mab; accepting her offer of the Winter Knighthood in exchange for the power he needs to save his daughter.
The Leanansidhe, who has been assigned to aid in this quest by Mab, joins in the planning. With help from his godmother, Sanya, Karrin, Thomas, Molly, Susan and Martin, they set out on the first leg of the journey to where his daughter is being held. Along the way, Harry uses a sending stone to communicate with Ebenezer, informing him that Maggie is his daughter. Upon learning this, Ebenezer changes his mind, encourages Dresden to do what he needs to do, and reveals that he is actually Dresden's grandfather: He knows what it is like to lose a child.
Confronting the Red Court, the Red King grants Harry an audience. The Red King agrees to allow Dresden to duel Arianna in exchange for Maggie's life. After Dresden finally kills her, the Red King refuses to honor their agreement. The group then engages in a seemingly hopeless battle against the Vampires, only to be joined at the height by the Grey Council -including Odin and Ebenezer- and an army of birdlike creatures from the Nevernever. After a seeming betrayal by Martin that causes Susan to lose control and drink his blood, Dresden learns that all of Martin's actions have been to put someone in a position to destroy the entire Red Court in one blow, namely Susan. Dresden carries Susan to the altar and cuts her throat, unleashing the Bloodline Curse upon the Red Court and killing every last one, now that Susan had become the youngest vampire of the Red Court. The few half vampires who are not killed by the removal of their vampire halves, as well as the Red King's Mortal followers, are almost all destroyed by the angered captives of the Red Court.
In the aftermath, Dresden realizes he can never provide the sort of home for Maggie he wants her to have and asks that she be placed in the safest possible place, and give her up to Father Forthill. Later, recovering on Thomas's boat the Water Beetle, Dresden goes onto the deck to get some air, only to be shot and fall into Lake Michigan.