- Guardians of the Galaxy
- Black Order
- Kree Empire
- Ronan the Accuser
Following the Extremis Virus' rampage, the Guardians of the Galaxy (Nathan Quill / Star-Lord, Gamora / Zoe Gillan, Cougar, Drax the Destroyer, Sebastian Allan / Rocket Raccoon, Groot, Nebula, and Yondu Udonta) are with Reed Richards / Mr. Fantastic and Susan Storm / Invisible Woman travelling in space in the purpose to seek answers about where the Extremis originated and/or who created it. Using a sample of the Symbiote to track its source down, the group end up on the planet D'Bari IV. Upon arrival, they are attacked by the Phalanx, cybernetically enhanced symbiotes which have been assimilating planets and their inhabitants including most of the D'Bari, on the behalf of their creator and master Ultron.
The heroes survive the attack, but their ship is damaged, leaving them stranded on the planet. After finding some shelter, the Guardians overhear more from Richards and Susan about Ultron, who is an Artificial Intelligence android created by Thanos to be his lead scientist for the Black Order. Rocket manages to hack one of the destroyed Phalanx spawns and discover that the Phalanx are controlling the planet through four technologic towers, which they plan to destroy to disable the Phalanx. While Rocket, Nebula and Yondu stay to repair the ship, the others move on, with an mysterious, curious figure following them. The group reaches the towers, while they are also alerted of an incoming Kree ship piloted by Minn-Erva, who was sent by Ronan the Accuser to harvest D'Bari IV for Ronan's future plans. Just as they are attacked by a berserker Phalanx unit, the heroes are joined in by Mantis, a young alien girl with empathic powers and the only inhabitant of D'Bari IV who was not mutated by the Phalanx. To their surprise, Mantis was not possessed by the parasites, because she is immune to their powers. From his research towers, Ultron observes Mantis' actions and, noticing ow powerful she is, announces to all Phalanx of the great threat she imposes, and orders them to kill her immediately.
The Guardians opt in standing in Mantis' defense and keep her safe in a nearby shelter. As Star-Lord and Mr. Fantastic formulate a plan to dispose of the Phalanx, Gamora and Invisible Woman stand next to Mantis, who is afraid of interacting with the D'Bari because of her fear of being considered a freak to them, and has been living as an outcast with no place to call home, which sadly reminds Nebula (who was at the time listening to their conversation) of her own experience in Zen-Whoberi before she joined the Guardians. As they continue formulating plans to stop the Phalanx, the Guardians also begin discussing what to do for Mantis, starting by seeking answers about who her parents are. Just then, Minn-Erva arrives on her ship and prepares it to mine the planet's molten core, but the ship is attacked and possessed by the Phalanx and Minn-Erva's crew members are infected and possessed, forcing her to flee outnumbered. Ultron plans to convert the ship into a doomsday device, but not before Yondu, Nebula and Rocket finish restoring Star-Lord's ship, with the group deciding to take the fight to Ultron.
As Star-Lord commands his ship to fire at the possessed Kree ship, the Guardians continue fighting the Phalanx, with Mantis (whose plant-based physiology is toxic to the organism) being the most efficient fighter, capable of freeing the infected D'Bari from their possessions via physical contact. This makes Star-Lord and Mr. Fantastic deduce that the Phalanx are vulnerable to botanic substances, which explains why the Phalanx could not approach the heroes while they were hidden in the trees and grass. Ultron attempts to attack them directly, but is held back by Groot, distracting him while Rocket begins working on a virus which will disconnect Ultron from the Phalanx. Minn-Erva attempts to shoot at Star-Lord's ship to save her own, but is stopped by Invisible Woman and beaten up by Gamora and Nebula. Mantis is likewise able to destroy the Kree ship by crushing it with countless vines after she takes a deep spot on a area where she remembers to have made her first steps. Groot and Rocket manage to defeat Ultron and inflict the virus on his network, disintegrating the Phalanx and and the Kree ship entirely. Ultron flees, but kidnaps Minn-Erva to be used as a slave for Thanos. The Guardians (joined by Mantis) return to Earth pleased to have ended the Phalanx threat, but knowing that Ultron and Thanos have yet to be dealt with. Back on Baxter Institute, Nathan and Zoe continue their studies while hearing that Mantis has found a new home with Groot and Nebula at Pegasus Z. Meanwhile, Ronan overhears of Thanos' abduction of Minn-erva, and takes his actions as an act of war.
- Scott Menville as Star-Lord / Nathan Quill
- Laura Bailey as Gamora / Zoe Gillan
- Jessica DiCicco as Mantis
- Troy Baker as Rocket Raccoon / Sebastian Allan
- Travis Willingham as Groot
- Erica Lindbeck as Nebula
- William Salyers as Yondu Udonta
- Alan Tudyk as Mr. Fantastic / Reed Richards
- Catherine Taber as Invisible Woman / Susan Storm
- Michael-Leon Wooley as Thanos
- Jim Meskimen as Ultron, Phalanx
- Nika Futterman as Minn-Erva
- Jonathan Adams as Ronan the Accuser
- "Spirit" by Beyoncé