Major story spoilers ahead.
The fight before escaping the prison
The game starts of with the protagonist, Marcus Fenix being freed from prison by his close friend Dominic Santiago. They both manage to escape the Locusts and the prison before it is destroyed by a Corpser. Both of them then proceed to meet up with their colleagues in Delta Squad, Anthony Carmine and Minh Young Kim. The Delta squad is ordered to find the Alpha Squad and the resonator; a device which maps out the Locust underground tunnels.
While proceeding towards the last known location of alpha squad, Carmine is killed by a Locust sniper. Later the Delta squad meets up with Augustus Cole, a member of Alpha Squad who says that the rest of the Alpha squad are at the Tomb of the Unknowns. Their transmissions get interrupted by the Seeders. Marcus then destroys them using the Hammer of Dawn to continue on to the Tomb.
Marcus after defeating the Berserker
They meet up with three more Alpha members on their way, Daimon Baird, Gyules and an unnamed Gear and get attacked by Locusts. In this process Kim is seperated from the others and gets killed by General RAAM. The unnamed Gear then gets killed while providing cover fire so that his fellow Gears can get inside the Tomb of the Unkowns. After the death of two of his squadmates, Gyules gets killed by a Locust Berserker inside the Tomb while trying to escape it. Marcus then kills it using his hammer of dawn. Confirmation of the resonator's safety is sent to the headquarters and Marcus is put into the charge of the Delta squad instead of Kim. They are then ordered to reach Lethia Imulsion Facility.
