It's pretty simple I think. Skolas escapes from the nine somehow (I think they released him or something) and then he's all like"I'm the leader now" So he's trying to take over all of the fallen and shit like a dictator. And Variks is all like "yeah he's gone cray" So then he goes to get the Vex time machine shit to grab more fallen from all different moments of time to get a big army. And we come in to try and stop him and we do. And he gets sent to prison. So then I guess we go to the prison to kill him for lulz (I mean why do we have to kill him, he's already in prison? It's like going into our real life prison and just murder the prisoners, what's the point?) So yeah we kill him and that's the end of the story cuz Skolas is dead.