The secrets behind the mysterious Mr. Oz are finally revealed here in this prelude to Geoff Johns's epic THE DOOMSDAY CLOCK event! From the pages of DETECTIVE COMICS and ACTION COMICS, Mr. Oz has been plotting against DC's heroes since DC Universe: Rebirth. The agents of the mysterious villain begin to move as the Man of Steel works to stop the chaos they unleash in Metropolis and across the globe. But when Mr. Oz steps from the shadows, his identity rocks the Last Son of Krypton to his core. Who is he? And how will his unveiling affect the events of THE DOOMSDAY CLOCK? In a prelude to the biggest event in comics history, Dan Jurgens and James Tynion IV bring together one of the great mysteries of the DC Universe and lead into Geoff Johns's epic story! Collects stories from DETECTIVE COMICS and ACTION COMICS.