Day One

Day One is a short story in The Dresden Files series by Jim Butcher. It is set after Skin Game. It can be found in the anthology Unfettered II.

Plot
Waldo Butters is training in Bucktown with Michael Carpenter, when he notices a homeless guy on a park bench. Apparently overdosed on drugs, the guy refuses hospitalization, but Butters and Carpenter call an ambulance anyway.

At the hospital, much to Butters' surprise, the guy, named Stan, is bedded in a pediatric wing, with eight children with symptoms similar to his. A Dr. Miyamune is attending to them and Butters recognizes her as the source of the sick's trouble. A baku, appearing as a woman of asian descent with incongruous blue eyes, she originally was an eater of children nightmares, which cumulated in her, causing her to become a malevolent monster, somewhat akin to those White Court vampires which feed on fear. Waldo Butters engages her in battle and kills her, at the price of his eyeglasses.