Master Chief John-117 leads his team of elite Spartans against the alien threat known as the Covenant. In the wake of a shocking event on a desolate planet, John cannot shake the feeling that his war is about to change and risks everything to prove what no one else will believe that the Covenant are preparing to attack humanity's greatest stronghold. With the galaxy on the brink, John embarks on a journey to find the key to humankind's salvation, or its extinction the Halo.