On Peter Quill's 13th birthday, Chitauri warriors attack his home, kidnapping him and killing his mother Meredith. Many years later, Quill—now a mercenary called Star-Lord—is the leader of the Guardians of the Galaxy, a group of "heroes for hire" hoping to make money during their adventurous wanderings around the galaxy. In the years following a massive interstellar war, the Guardians have accepted a job to capture a rare monster for their patron, Lady Hellbender. They head to the Quarantine Zone, a restricted sector established by the Nova Corps to store debris from the war. However, they are forced to flee the zone when Quill accidentally releases an alien entity from a yellow gem.
The player can attack enemies with elemental guns which have four shooting modes; ice shots temporarily freeze enemies, lightning shots stun them, wind shots pull in faraway enemies, and plasma shots deal fire damage to boss characters. The other Guardians, including Gamora, Rocket Raccoon, Groot, and Drax the Destroyer, are non-player characters controlled by artificial intelligence, but the player can issue commands to them during combat. Each Guardian has four unique abilities which can be chained to inflict more damage; Groot uses his roots to immobilize enemies, Rocket deploys various explosives and bombs, Drax can easily stagger enemies with his strength, and Gamora uses her sword to deal powerful melee damage. Players can also use environmental features to their advantage, for instance, by instructing Drax to hurl a large boulder at enemies.