Batman #609, "Hush, Chapter Two: The Friend"
Oracle and Huntress save Batman after his fall, and manage to bring his unconscious body back to the Batcave. Unable to save Batman himself, Alfred contacts Dr. Thomas Elliott, a childhood friend of Bruce's. This issue introduces a key figure in the Hush saga via a flashback sequence, rendered in a unique art style from Jim Lee. Overall, this issue doesn't have much beyond the exposition, but it'll be key for the payoff for this story.