Now let me warn you, it's not a big full out detailed plot description like so many people want. So if you're expecting that, lower your hopes just a little bit. This description came off a recently listed Transformers 3 Push-Pops [Board book]. Yeah, I'm not sure exactly what it is either but it's description reveals the overall plot of the next film:
The Autobots, led by Optimus Prime, are back in action, taking on the evil Decepticons, who are determined to avenge their defeat in 2009’s Transformers Revenge of the Fallen. In this new movie, the Autobots and Decepticons become involved in a perilous space race between the U.S. and Russia, and once again human Sam Witwicky has to come to the aid of his robot friends. There's new characters too, including a new villain in the form of Shockwave, a longtime "Transformers" character who rules Cybertron while the Autobots and Decepticons battle it out on Earth. Three spreads of this colorful book feature large fold-out panels that reveal panoramic battle scenes and towering Transformers. Three of the spreads also feature dramatic pop-ups that put readers right in the middle of all the action.

Like I said, it doesn't get very specific, but at least we have an idea of what the film will be about. Unfortunately it doesn't explain how any of these events come to happen, but fans will have plenty to pick over I'm sure. Now, let even more speculation begin!
-Jordan