Galactic War 1

This story starts out 5000 years plus in the future on a distant planet and someone discovers there is a threat to the entire universe, an ultimate weapon has been unleashed in the process finds out the own way to deal with this problem is to travel to earth. In the process meet someone who can assist only there is the small snag the item they require does not exist anymore. So they travel back in time to acquire this item and in the process run into a few problems, after threat is thought to be neutralized they track down those who are responsible and get more than they bargained for.