The game begins with the player's Ghost resurrecting them as a Guardian, after having been dead for an unknown length of time. The Guardian is quickly forced to fight Fallen who have inhabited the ruins of the nearby Cosmodrome in Old Russia. The Guardian, with the aid of their Ghost, is able to secure a jumpship and escape to The Tower that houses the Guardians on The City border.
After being outfitted and introduced to the Vanguard, and Gunsmith, the duo learn from Amanda Holliday that their Arcadia Class Jumpship is missing its Warp Drive, a component necessary for interplanetary travel. Due to the scarcity of the part and flyable jumpships in general, the Guardian is forced to return to where they found the ship in an attempt to find the part.
When they return to the Cosmodrome, the duo begin their search. They quickly learn from an old terminal that there may be a Warp Drive where they first found the jumpship, in Dock 13. As the Guardian approaches, their Ghost detects a Warp Drive, which has unfortunately already been scavenged by the Fallen. With no other feasible option, the Guardian pushes forward and engages the Fallen, defeating the Fallen Archon, Riksis in the process.
Upon their to The Tower, the duo meets The Speaker, who explains how The Traveler, in its dying breath, created the Ghosts to seek out those who can wield its Light as a weapon, to protect humanity against the mysterious force known as The Darkness, which crippled The Traveler in its last encounter. He then explains how The Darkness has returned and that humanity will not survive this time. The Guardian, wanting to help, is told to join the others fighting back against The Darkness on Earth and beyond.