Warning: Spoilers ahead for The Flash #21.
Flash #21, the second chapter of "The Button," makes it official (along with a few other issues out this week) - the history of the post-"Rebirth" DCU goes back many years and includes adventures from before the beginning of the "New 52."
The Flash #21, written by Joshua Williamson with art by Howard Porter, not only continues the story of "The Button," but busts the door open to a much longer timeline for this reformed DCU. In just a few panels and Easter eggs, the issue brings several fan-favorite characters and concepts back into canon, including the "Bwa-ha-ha" history of the Justice League, events from the JLA run of Grant Morrison (which Porter illustrated part of), and even the Batman mind-wipe from Identity Crisis.
There are hints about the Justice Society of America, a tease about Batman's time-traveling after Final Crisis and what appears to be a new/classic version of how the Justice League was formed.
Let's dive in to super-spoiler territory and look at the issue.
Remember the Justice Society tease from DC Universe: Rebirth #1 almost a year ago? We hadn't seen the elderly Johnny Thunder since, but he reappears on the first page of The Flash #21.
Standing on the roof of his nursing home during a thunderstorm, Johnny yells, "Where are you Thunderbolt? CEI-U! Please!"
The orderlies grab him and decide to "up" his meds, but Johnny says the "lightning said we need to find my friends!"
"We lost the Justice Society!" Johnny says. "It's all my fault!"
Then readers get a review of what happened so far in "The Button" - the first chapter in last week's Batman #21 - with Flash/Barry Allen using his CSI skills to retrace the fight between Batman and Eobard Thawne/Reverse-Flash.
Thawne's body, half of his flesh seemingly vaporized, lies on the floor of the Batcave, where he collapsed last issue after having touched that Watchmen Button that Bruce has been investigating.
Taking a moment to remember his dead mother (whom Thawne killed), the Flash notices that Thawne's body is covered in the unique energy signature of the Speed Force - an important clue, since the villain usually pulls from the Negative Speed Force, which leaves a different signature.
Barry wonders if perhaps he killed Thawne in the future?
Alfred says the Batcave's surveillance technology was disabled when Reverse-Flash showed up, probably affected by Thawne's lightning. The Flash needs to talk to the one witness to the murder - Batman.
Road Trip Time
More review of Batman #21 follows, as a beaten-up, bed-ridden Batman tells the Flash about Thawne's statement (just before he died) that he saw "God." He tells Barry about the reaction between the Psycho Pirate mask and the button, which caused a "ghost" of Flashpoint Batman (Thomas Wayne) to appear.
Bruce once again reiterates the new status quo of Flashpoint - that it did not cause the "New 52" reboot, and that "whatever messed with time was doing so long before Flashpoint."
And Barry remembers how he also saw a "ghost" of sorts - what he calls the "Helmet of Mercury." The event, which happened in The Flash #9, caused a "wave of calm" and "a new hope" in Barry at the time.
Two ghosts? Connected to the Speed Force?
Sounds like it's time for a road trip!
Barry runs off, but his thought box reveals to readers that Thawne's body also had "massive amounts of the same radiation we found on the Button" - a fact he doesn't share with Batman.
Where's Flash running to? The Justice League Watchtower.
Whole New Continuity
Inside the Watchtower, readers get their first hints about the revised timeline of "Rebirth."
In a room filled with artifacts - a room Barry says is called "the hall of lost and found" by Hal Jordan - are a slew of Easter eggs, from Martian Manhunter's suit to Destiny's book to Lobo's hook to the "Worlogog" encountered in several past Justice League stories.
The room's contents make it official that the Justice League has been around a long time in this newly formed "Rebirth" continuity. There are Justice Society and Justice League International hints like Booster Gold's Skeets, Hourman II's cowl, a Doctor Fate helmet, a Star-Spangled Kid costume and - looming large over the whole room - the Timeship used by Hourman III, the android hero from the 853rd Century.
There's even one of Blue Beetle's Bugs in the room, verifying that Ted Kord was once part of the League and seemingly bringing the beloved JLI history back into canon.
Barry runs through the Watchtower to find his Cosmic Treadmill, last used by the Flash to go back in time and change history into the Flashpoint universe.
Now Barry wants to use the treadmill to find who killed Thawne and is manipulating time.
But he's not going on this road trip alone - Batman has left his brief convalescence to follow Barry to the Watchtower.
After Barry's warnings about time travel, Bruce mentions that he's traveled through time before - what some could read a possible nod toward his post-Final Crisis travels, but could instead refer to Bryan Hitch's recent Justice League run.
So the two depart on the treadmill, Barry running to power it and Batman just barely holding on with a grappling hook.
Immediately, Barry says something is different. "I've never seen anything like this before."
The pair is traveling through a blue-tinted, turbulent storm of some type, with purple/blue, vein-like flashes running through it.
The following panels show scenes that appear to be from the past.
First is the formation of the Justice League, with Superman, Batman, Aquaman, Flash, Wonder Woman, Green Lantern, and Martian Manhunter. "That's not how the Justice League formed," Flash says. Batman questions whether they're seeing alternate worlds.
As Flash sees scenes that show Batman's Identity Crisis mindwipe and Barry's own death, Batman and Flash realize that perhaps these are from the "stolen" years.
"I don't think these are alternate realities," he says. "These are from our universe."
The storm intensifies, and Barry tries to outrun it. But the treadmill is pushed out of the storm, into the real world again.
As Flash notices that the treadmill is destroyed, Batman realizes they're in the Batcave. Only… something's off about this Batcave.
Bruce is confused. It's a rudimentary Batcave, and someone has placed a gun under a glass dome. The gun, Bruce says, is from the night of his parents' murder.
"I never recovered it. How is it here?" he asks as he takes off his cowl. "Barry, where the hell are we?"
A voice replies, "I did this all because of you, son."
And the final page shows Thomas Wayne in his full Flashpoint Batman costume, standing before a similarly costume-clad Batman, with Flash obviously disturbed that he's caused this event.
Next, the teaser at the bottom of the page says, will be "Flashpoint! Batman, father & son!"
"The Button" is scheduled to continue in May 3's Batman #22.