Once Upon an alternate reality Louis sacrificed himself instead of Bill...
Though Louis had taken an overdose of pills, allowing him to be revived about two and a half minutes later.
Louis was angry at Francis, Bill and Zoey for what he sees as abandoning him and leaving with the L4D2 survivors in Jimmy Gibbs' car.
In this universe all the survivors are together (expect Louis) one small issue; Ellis left his hat in The Parish Chapter 3.
So the original survivors decide to go back through the 2nd game campaigns to retrieve it.
Francis did take some convincing because of how much he hates "Ellis' Hat" but he came along in the end.
Louis gets word of them coming back through whitaker and Virgil, and is out for revenge!
He has managed to break into and abandoned lab in the Time 2 Die campaign and cloned himself. Now the L4D1 survivors need to get Ellis' hat and survive Louis and his clones at the same time!!!!!