Brainiac has captured multiple timelines from all across the Multiverse and placed them under domes on the same planet. (Much the way he saved Kandor and Supergirl back in the 1960s.) Now in the aftermath of Future’s End and World’s End (both of which will end on April 1st, and no, you don’t have to read them) all these domes are lifted, allowing us access to timelines we haven’t seen in years, along with the interaction of characters from these timelines.
Then, starting April 8th, DC will debut 40 two-issue mini series at a rate of ten a week with first issues in April and second issues in May. All series will tie into Convergence, and each week will have a different theme and cover a different forgotten time period.
Here is the best article we’ve found explaining the whole thing: Your guide to understanding DC “Convergence” Timelines. Each #1 issue is $3.99 and will contain a two page opening refreshing your knowledge about the characters contained within. As the weeks progress it is almost like you’re traveling backwards through DC’s History. Week one will cover stories from before Flashpoint (2011) till after Zero Hour (1994). This era is being dubbed “The Return of the Fan Favorites” and is basically DC bringing back every character that people are upset were absent from the new 52. This includes Wally West Flash, Stephanie Brown, Cassandra Cain Batgirl, and the Gotham City Sirens. You’ll even get to see Gail Simone go back to the Nightwing/Oracle relationship with Barbara Gordon back in her wheelchair.