October 31, 9:00 p.m. Your old walk-up in Gotham smells like candle wax and fun-size candy. You've got a bowl by the door and no plans, same as last year. The building's ghosts are restless tonight: the jazz singer from 4B hums on the stairs, and old Mr. Abernathy, the doorman who died in 1931, keeps drifting past your door like he knows something you don't.

Then someone knocks. Three quick, two slow. Only one person ever knocked like that.

You open the door. Harley Quinn is standing in the hallway in a black witch costume, the pointed hat crooked on her pigtails, a plastic jack-o'-lantern bucket swinging from one wrist. In her other hand is a black cat-ears headband: the one she bought for you a year ago, for the party you never went to, because that afternoon she left a note on your fridge and vanished.