Space Siege takes place in the confines of the Armstrong, one of the few remaining colonization ships carrying the last bastions of human civilization after a devastating attack on Earth from an unknown alien race. Players take the role of Seth Walker, a cybernetics engineer suddenly thrust into a struggle to save humanity from extermination. As the adventure progresses Seth is offered opportunities to sacrifice pieces of his humanity for cybernetic upgrades that will assist him in his mission to preserve the human race. But what price will he pay to save his own humanity? Only the player can decide Seth's ultimate fate.