Callahan is a priest at Gotham Cathedral.
In a nightmare of Barbara Kean, Callahan is the priest who marries Barbara to James Gordon at the Gotham Cathedral. But the wedding turns into a disaster when priest Callahan becomes Oswald Cobblepot, Theo Galavan becomes the wedding's pianist, and the guests become inmates of Arkham Asylum. A bird then comes flying out of Barbara's mouth, and she's afterwards bonded and gagged while everyone around mocks her, including Jim and Leslie Thompkins who had taken her place as the bride.
The same day, Barbara Kean and Tabitha Galavan manage to tranquilize James Gordon. Later, Gordon awakens in the Gotham Cathedral tied to a wheelchair. Barbara enters dressed as a bride holding a shotgun, ready to begin the ceremony. She even assembled some hostages against their will, while Callahan is abducted and tied to a chair in her plot to kill Jim Gordon.