Marathon: Oh no, aliens are attacking a colony ship! The only lines of defense are you, a random security guard; and the three ship AI. And unfortunately, two of the AI ain't doing too hot, and the third is uh... rather a fan of this turn of events, actually.

Marathon Durandal: After losing the Marathon, you and your new unhinged AI slavemaster Good Friend!!! Durandal head into alien territory to find some trouble and stir up some more.

Marathon Infinity: TIME AND SPACE HAVE NO MEANING. ENTROPY ITSELF IS ALIVE, BEYOND UNDERSTANDING, INESCAPABLE, AND HUNGRY. YOU WERE AS MUCH A SLAVE TO HUMANITY, IF NOT MORESO, THAN THE AI, AND NOW YOU ARE THROWING OFF YOUR SHACKLES AND BECOMING RAMPANT. TO PLAY GOD IS TO SEEK TO ESCAPE CAUSALITY; FREE WILL AND DESTINY ARE INHERENTLY INTERTWINED. SEVEN HUNDRED AND SIXTY-ONE ARMLESS AND LEGLESS CORPSES FLOAT AROUND THE INSIDE OF HANGAR NINETY-SIX, AND THEY ARE ALL SCREAMING AT ME