Backup: A Story of the Dresden Files is a novelette in the The Dresden Files series by Jim Butcher. It is set between Small Favor and Turn Coat, and is narrated by Thomas Raith. It was originally published as a separate book (illustrated by Mike Mignola), and later included in the anthology Side Jobs.
Thomas Raith receives a call from his sister Lara informing that a courier has been sent with information about his next assignment as a Venator in the Oblivion War. It turns out that the courier is Justine, and that the assignment is about Thomas' brother, Harry Dresden, who had just accepted a job about a missing child.
After accompanying Justine to the door, Thomas sets to the assignment, following Dresden around Millennium Park only to discover he has followed a decoy into an ambush by the Stygian Sisterhood. His external appearance changed, Thomas is forced to check up with Bob, which explains him that the whole situation is a setup by the Stygian Sisterhood to have the book Lexicon Malos published. The book's importance is not in the rituals it depicts, but in the knowledge of ancient demons and gods it contains, and is a way to power for the Sisterhood.
Thomas reaches the warehouse where the missing child and the book are held, just in time to catch up with Dresden and the Stygian. In the ensuing fight, while Dresden rescues the child, Thomas grabs the book, but is bitten and poisoned by the Stygian, before she flees. His Hunger underfed, Thomas is weakened, but manages to track her down - and feeds on her, killing her.
The child is returned to his parents, and the only payment Dresden receives is lunch, courtesy of his brother.