Halo 4 is the seventh installment of the Halo franchise. The campaign starts out four years, seven months, and ten days after the events that occurred in Halo 3. Cortana is forced to activate John-117’s cryopod, due to an energy that passed through the aft section of UNSC Forward Unto Dawn. The Covenant boards the ship and John is thrown into action, despite his concern that he believed humanity had ceased fire with the Sangheili. Through all the battles with not just one Covenant ship, but an entire fleet orbiting a Forerunner world, Cortana realizes there’s a cruiser close to them that has its shield down and advises John to fire a tactical nuke at it. John does so and immediately, the explosion opens up a passage into the planet that activates a gravity well, pulling in every ship. Forward Unto Dawn is already weak prior to this, but now it just starts disintegrating and passing into the planet. While John and Cortana make their way to the escape pods, Cortana starts malfunctioning. To make matters even worse, a Covenant cruiser tears straight through the escape pods. On impact, the Spartan is thrown outside of Forward Unto Dawn, as the whole this passes through the opening.
John-117 gains consciousness, only to realize he is inside the planet. Cortana confesses to John why she keeps glitching and having behavioral problems. It’s due to her going into the first stages of Rampancy. Now their main goal is to find a ship, get back to Earth, and see if Cortana’s creator, Dr. Halsey, can fix her. They eventually fight their way through the Covenant to a localized Cartographer. Cortana says their location is a shield world called Requiem and that she is receiving a signal from an unknown source that is not the Covenant and suggests that they look for the signal. The signal ends up being bounced off of a tower near the plant’s core. Cortana manages to open a portal as close to the core as possible, right as a large number of new enemies appear.
Once John and Cortana are teleported closer to the signal, they find that it’s coming from UNSC Infinity asking for help. A satellite near the center of the planet is blocking the signal by two jamming towers. John defeats several groups of the new unknown enemy, while Cortana discovers the only intelligence she could receive from them is the word “Promethean,” and them being more advanced combat AIs than Sentinels. After John takes down the first tower, they find out that the Covenant is interested in something that’s hiding inside the core. They proceed in taking down the second tower to receive the full signal from the Infinity. The Infinity ship is going to enter the planet and Cortana needs a way to warn them away. They finally find the source of the signal, a giant spherical object, after fighting their way to the center of the Satellite. After trying to stop the signal, the sphere reveals a sole figure on a pedestal, the unknown figure introduces himself as The Didact. He declares that his people, The Forerunners themselves, are returning to the Galaxy after thousands of years. The Didact comments on how Humanity must still be weak, because the Covenant does not answer to Humanity and are still unworthy of the Mantle.
Chief escapes the Didact and joins together with Infinity, which had entered the planet. John fights off many Prometheans and Covenant, to finally join forces with Commander Thomas Lasky, Spartan Commander Palmer and scattered groups of Marines. Chief clears an LZ for a Pelican to pick them up to be transported to Infinity, where he fights even more intense waves of the Covenant. There, he is introduced to Captain Andrew Del Rio and Commander Palmer. Lasky, Palmer, and Chief are given a Mammoth and are sent on a mission to allow Infinity to escape Requiem. Through more battles against the Covenant, Chief and Cortana are separately taken by the Librarian, who explains to them that the Prometheans were once Humans and that the Didact is trying to escape Requiem and find the Composer, which he then plans to turn on Humanity. She helps accelerate Chief’s ‘evolution’ so he can survive the Composer. Once John and Cortana are reunited, they proceed outside of the Forerunners structures, to destroy the Didact, but they fail at their attempt. They return to Infinity, where Del Rio gives orders to leave Requiem, saying that they should return to Earth and inform FLEETCOM about what had occurred. Cortana and Chief try to negotiate with him, but the Captain orders that Cortana be decommissioned due to rampancy. Chief refuses to hand over Cortana, so the Captain orders both Lasky and Palmer to arrest him, but neither of them move. Lasky then assists John in escaping Infinity before they destroy the Didact for good, but they are unsuccessful and boards a Lich to follow the Didact into slipspace.
Chief, The Didact and a Covenant fleet, arrive at Halo Installation 03. Under the Didact’s control, the Convenant attack the UNSC science facility orbiting the Halo, that housed the Composer. Chief manages to get inside to grab a HAVOK bomb to destroy the Composer, but is too late, the Composer is fired and kills all on the base besides him. Chief takes a Broadsword to follow the Didact to Earth, where he is assisted by Infinity, which is now being controlled by Commander Lasky, in getting inside. There, the Didact fires the Composer, which begins and extermination of Humanity in New Phoenix. Cortana clones her rampant personalities to overload the Didact’s system, in order to bring it down. Chief puts her chip in a holopedestal, but Cortana’s chip is destroyed and she is put inside the Composer’s system. Cortana is able to barely communicate with John before helping him defeat the Didact and destroying the Composer. She then manages to use the last of her energy to form herself into a visible form and is able to finally touch John for the first time, but unfortunately it will also be the last time. Cortana dies right before the Composer collapses around them. A Pelican finds John within the space debris. At the end, Commander Lasky repeats a statement Cortana once said to John regarding the humanity of soldiers. The final scene shows John on Infinity’s Spartan deck, having his armor removed.