As it's a michael bay, in theory it just went, 'bang, wow, *explosions*, boom, 'where'd we put the storyline?' 'I dunno', insertcredits here. Although that may be just me.
Here's what IMDb put - A mechanic and his family join the Autobots as they are targeted by a bounty hunter from another world.
So basically the same story as all the other films.