Batman and Flash are currently at the heart of the single biggest mystery in the DC Universe. Last year's DC Universe Rebirth #1 ended with the revelation that the DC Universe has been manipulated by Watchmen's Doctor Manhattan. Now, DC is kicking off a new crossover storyline called "The Button," as the two greatest costumed detectives in the world join forces to get to the bottom of this mystery.

It Started With Flashpoint

Art by Andy Kubert. (DC Comics)

Batman #22 cover by Jason Fabok. (DC Comics)

The Watchmen and DC Universes Are Colliding

Art by Gary Frank. (DC Comics)

Before Watchmen: Doctor Manhattan art by Adam Hughes. (DC Comics)

The Comedian Visited the Batcave

Art by Gary Frank. (DC Comics)

Art by Dave Gibbons. (DC Comics)

Why are the DC and Watchmen universes colliding? How does all of this tie into the events of Flashpoint? We've put together a helpful guide breaking down everything we know about the mystery fueling "The Button."Everything happening in DC's current Rebirth status quo has its origins in 2011's Flashpoint mini-series. Flashpoint featured an alternate reality where Atlantis and Themyscira were at war and many familiar heroes like Superman and Green Lantern were dead or MIA. A de-powered Barry Allen found himself teaming up with Thomas Wayne (who in that reality became Batman after the death of his son) in order to restore the normal timeline. Barry eventually learned that he himself caused Flashpoint when he traveled back in time to prevent his mother's death. In the end, Barry undid that mistake and restored his reality, though not without some significant changes. Flashpoint became the catalyst for DC's streamlined New 52 continuity.While Flashpoint eliminated a great deal of existing DC continuity, it did strengthen the bond between Batman and Flash. Flash brought the Dark Knight a gift from the Flashpoint timeline - a letter written by Thomas Wayne. Bruce has always respected Barry as a scientist, but it could be argued that moment is when they became true friends. And it certainly set the stage for their shared investigation now.It also appears that Flashpoint itself will be returning during the course of "The Button." Both Reverse-Flash and the Thomas Wayne Batman are featured prominently in DC's preview art, suggesting that Bruce and Barry will have to travel back to where it all started. This will actually mark the first appearance by Eobard Thawne since Thomas Wayne killed him in the original Flashpoint.DC Universe Rebirth #1 dropped a number of bombshells, but none bigger than the revelation that the very fabric of the DC Universe has been altered by an outside force. That force appears to be none other than Doctor Manhattan. It turns out that Barry Allen wasn't responsible for creating the New 52 when he reversed Flashpoint. Instead, Manhattan used that moment as a way of gaining a foothold into the DCU.It's Doctor Manhattan who used his seemingly limitless power over reality to manipulate the DC timeline and literally remove a decade of time. That's why the New 52 resulted in heroes de-aging and losing many of the critical relationships that once defined them (Superman and Lois Lane's marriage, Green Arrow and Black Canary's romance, etc.). Manhattan seems intent on performing a grand, cosmic experiment, testing the bonds that exist among DC's heroes and leaving them vulnerable to attack. The driving idea behind DC Rebirth is that our heroes have to reclaim the love, joy and optimism they lost in order to stand a fighting chance against this all-powerful, very cynical foe.Naturally, there's still a lot we don't know about the role of Doctor Manhattan in DC Rebirth. We don't know why, after the profound journey he experienced in the original Watchmen, Manhattan would take such a dark turn. We can't even be sure he's the true mastermind of this plot. Perhaps another character (Ozymandias?) is either manipulating Manhattan or simply mimicking his powers. Nor do we expect "The Button" to address all of these questions. But at the very least, this story will be a critical step in the journey towards understanding the true threat our heroes face.So why is this crossover called "The Button"? It ties back to one of the final pages in DC Universe Rebirth #1, where Batman traveled into the depths of the Batcave and uncovered a strange object wedged in a rock. That object turned out to be a blood-stained smiley face button. If you don't understand the significance of that, it's probably time to give Watchmen a read.This begs all sorts of questions. Was it The Comedian himself who left his calling card for Batman to find? If so, to what end? And for that matter, how is Edward Blake alive when his death was the spark that set the wheels of Watchmen in motion in the first place? We can't imagine Manhattan wants DC's heroes to become aware of his meddling, so it's possible the blood-stained pin was left as a message of warning, one that will allow Batman and Flash to rally their fellow heroes before it's too late.This also leaves us to wonder just how many other Watchmen characters might be alive and active within the DC Universe. It's very likely that Ozymandias made the jump (more on that later). But what about Nite Owl, Silk Spectre or Rorschach? Is everyone in on Manhattan's plan, or would this be an opportunity for, say, a resurrected Rorschach to succeed where he failed in the original Watchmen? How would refugees from the dark, cynical Watchmen universe react to a world where people actually look up to their costumed heroes? That sounds like a pretty worthwhile story in itself.

Head to page 2 to learn why the Flash family is growing again and why the DCU now has three Jokers.