一次致命的撤離任務標誌著士官長與星盟戰爭的轉變。在致遠星上，新政權接手了艦隊司令部。約翰感覺到家附近迫在眉睫的威脅。

約翰在尋找失蹤的斯巴達戰士時將銀隊推向極限；凱擔心約翰的穩定性。當關發現索倫不在時，瓦礫是一個更危險的地方。哈爾西尋找綁架者的身分。

約翰和銀隊開始執行一項未經批准的任務。萊拉、關和凱斯勒必須逃離索倫叛變的手下。艾克森從 Cortana 那裡收到了令人不安的情報。攻擊的威脅迫使艾克森做出不可撤銷的決定。

失敗後，倖存者努力收拾殘局。在荒涼的阿萊裡亞星球上，約翰正應對前所未有的損失。索倫和萊拉尋找失蹤的兒子。當仲裁者變得不耐煩時，馬克小心翼翼地行事。

John seeks revenge on a secret ONI planet. Perez trains to become a new kind of soldier. Kai finds herself torn between her Spartan code and her loyalty to Master Chief. Makee turns to Cortana for help in her search for the Halo.

John-117 comes face to face with Makee. A revelation leads Ackerson to question his loyalties. Soren and Laera's relationship begins to fracture. Halsey, Kwan and Miranda work to solve a mystery.

The climactic battle for the Halo begins. John makes a fateful choice. Soren and Kwan undertake a rescue mission. Halsey and Miranda unleash an ancient horror.