在未来的约500年后，人类社会高度发展，并已实现向外太空的殖民。而在这一过程中，新的危机威胁着人类的存在。此时此刻，托马斯·拉斯基（汤姆·格兰 Tom Green 饰）还只是一名殖民星球军事学院的学生，他与迪娜（Kat de Lieva 饰）、Sully（Masam Holden 饰）每日进行艰苦严苛的训练，在此期间他一面饱受神秘疱疹的困扰，一面又对战争的本质产生之一。日常与身为地狱伞兵的哥哥通话给他仅有的安慰。直到某天，哥哥战死沙场，托马斯的去留也到了决断时刻。这一夜，未知的外星生物入侵学院，造成巨大的伤亡。危难时刻，战场之神士官长降临…… 　　本片根据同名电子游戏改编。In 2525, as mankind has begun to colonise space, a group of cadets are training to fight against human insurrectionists. One of these cadets, Thomas Lasky, has doubts about his abilities as a soldier and his convictions for this war. Whilst he struggles with himself, the planet is invaded by an unknown alien race. Reeling under the assault, Lasky and his squad mates are rescued by John-117, one of the UNSC's legendary SPARTAN-II super-soldiers. John must inspire Lasky to fulfill his potential as a soldier and a leader to fight against an enemy deadlier than any that humanity has faced before.