Things did not go so well last time. Sure they stopped Magneto but they didn't fix the problem. Now they are in the desert and giant robots are trying to kill them. That is ok though because Polaris opens up a can of whoop arse on them.
This time around you find that Cerebro has been corrupted by Ultron and destroyed almost all human life on the planet. That is the short short version. Stop the machines and give humanity a chance.
Should be no problem right? This is the Exiles, are you nuts?! Nothing is ever that easy. If you need proof of that just skip to the last page for the oh sh!t moment.