See how the fates of Batman and Dylan Dog intertwined in the past through their lethal nemeses: The Joker, the Clown Prince of Crime of Gotham City, and Professor Xabaras, a mad genius with a taste for bringing the dead back to life! Joker is in London to seal a hellish pact with Dylan Dog’s nemesis, the Mephistophelian Xabaras! The doorbell of Craven Road No. 7 screams, and beyond the doorway Bruce Wayne appears. For the Nightmare Investigator, an incredible adventure begins side by side with the Dark Knight. They'll have to forge an uneasy alliance, putting aside their differences in order to successfully confront and defeat an evil that comes from the past...