here is a brief plot line for TRANSFORMERS 2 REVENGE OF THE
FALLEN.
Autobots believing that peace was possible finds out that Megatron's
dead body has been stolen from the US Military by Skorpinox and
revives him using his own spark. Now Megatron is back seeking
revenge and with Starscream and more Decepticon reinforcements on
the way, the Autobots with reinforcements of their own, may have more
to deal with then meets the eye.
Decepticon forces return to Earth on a mission to take Sam Witwicky
prisoner, after the young hero learns the truth about the ancient origins
of the Transformers. Joining the mission to protect humankind is
Optimus Prime, who forms an alliance with international armies for a
second epic battle.
Here is the Offical Movie website and trailer