The plot revolves around the player switching between the mainstream Marvel and the Marvel 2099 universes, playing as both Peter Parker, aka the Amazing Spider-Man, and Miguel O'Hara, aka Spider-Man 2099, to try and prevent a catastrophe resulting from Peter Parker's untimely death, caused by an evil scientist from the 2099 universe. It's been stated that the actions of Peter Parker can affect the the world of Miguel O'Hara. An example of this is that if Peter Parker was to destroy a robot prototype, the finished robot wouldn't exist in Miguel O'Hara's time.
According to Marvel.com during the WonderCon 2011 panel, via Wikipedia:
Josh Keaton, who voiced Spider-Man in The Spectacular Spider-Man and Marvel vs. Capcom 3: Fate of Two Worlds and as well as Ultimate Spider-Man in Shattered Dimensions, provides the voice of the Amazing Spider-Man, while Spider-Man 2099 is portrayed by Christopher Daniel Barnes, who played Spider-Man in Spider-Man: The Animated Series and Spider-Man Noir in Shattered Dimensions.
Spider-Man: Edge of Time is set to hit the platforms on Fall 2011!