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 humanitys greatest stronghold. With the galaxy on the brink, John embarks on a journey to find the key to humankinds salvation, or its extinction — the Halo.