The year is 2201, one year after the Star Force returned to Earth bringing the Cosmo DNA device which rid it of the radioactive pollution caused by Gamilon's planet bombs. Since that time, no longer threatened by outside forces, Earth has recovered and expanded its naval power and terrirory to the periphery of the Solar System. Most of the Star Force crew are assigned to various posts on Earth, although the Argo is currently on assignment as the flagship of the Solar System's peripheral defence patrol fleet. Commanding it is Deputy Captain Derek Wildstar.
As the Star Force reunites to honor Captain Avatar's memory, Derek Wildstar says that he scouted what he thinks is a new and potentially very powerful and dangerous enemy. He then goes to the Andromeda and confronts Captain Gideon, who turns out to be one of his former instructors, about the near-miss in space. Gideon says that even though the Argo had landing priority as a returning spaceship, it still would have had to yield to the Andromeda because the latter was Earth's highest-ranking starship. Despite Wildstar's protests, Gideon simply tells him he will "learn the hard way."
Sandor and Wildstar try to decode the message Wildstar received, but the best either of them can determine is that it appears to be a jammed distress call vaguely warning the Earth of some sort of danger. Believing the message and the blackout may be related, Wildstar unsuccessfully tries to get the Earth Defense Force to listen. He then decides to take the Argo -- unauthorized -- out into space, even though he isn't fully sure there is a threat to Earth. Wildstar sends a message to the old Star Force crew, emphasizing that their participation in this mission is strictly voluntary since the mission isn't authorized. Sandor agrees to go, but Venture wants time to think it over. Nova is torn between letting Wildstar go and asking him to stay.
The Earth Defense Force learns that the Star Force's personnel have abandoned their posts and are boarding the Argo. It sends a message to the Argo ordering those on board to leave the ship and return to their posts immediately. Derek Wildstar acknowledges the message, but says the Star Force is made up of volunteers, so the crew might not obey. Meanwhile, Mark Venture meets with Dr. Sane and Nova at Captain Avatar's memorial and discusses his concerns about whether or not to go. Sane replies that the Star Force itself is special -- the crew is willing to take risks even if it isn't sure of the outcome.
As the Argo continues its journey to space, the trip is uneventful until the ship encounters three fighters from the moon's base station. Wildstar orders the bridge crew to their combat stations, then realizes that the fighter group is the Black Tiger squadron, led by his old crewmate Conroy. The Black Tigers have abandoned the moon base to join the Argo. Wildstar then discovers Nova on the ship. He admits he wanted her to stay on Earth for her own safety. Nova replies that she's a Star Force member too, and she wanted to go on the mission regardless of the danger.
The Argo answers a distress call from Space Marines on planet Brumas.
The Space Marines cause a flurry of problems for the Argo's crew, including disrepecting Nova's authority and literally creating a mess in the mess hall. Two sub-space submarines from the Comet Empire then attack the Argo. The Star Force destroys the submarines, but they still don't know what kind of enemy they are facing. Sandor has the ship land on a planet so the damage can be repaired. Meanwhile, the Argo's crew and the Space Marines get into a brawl and Wildstar and Sergeant Knox, the Space Marines' leader, get into a fist fight, which Dr. Sane breaks up. Dr. Sane says that Knox has to adjust to not only having been defeated at Brumas, but also to having had to relinquish command to Wildstar.
As the Star Force reaches the coordinates from Trelaina's last message, it receives a new message. The Argo warps to the new coordinates, but finds itself in the middle of a space cyclone. When the ship reaches the middle of the space cyclone, however, the Star Force finds the remnants of several ships that never made it out.
Wildstar makes contact with the Earth Defense Force but reports he hasn't been able to find out more about the Comet Empire. The EDF says that so far, nobody on Earth knows that the Comet Empire is more than just a comet. The Star Force then sees a Comet Empire ship, and Wildstar orders that the pilot be taken prisoner.
As the Argo continues to Telezart, it receives another message from Trelaina warning them of a meteor swarm. The crew verifies the swarm, which proves that Trelaina intends to help them. Back on Earth, the large comet is expected to arrive in one hundred days, prompting Captain Gideon to request five more ships similar to the Andromeda. Earth's population also begins to get suspicious when all non-defense space flights are grounded.
Desslok of Gamilon sets his plan into action against the Star Force.
After his initial plan to defeat the Star Force fails, Desslok of Gamilon implements one more trap...
The Star Force arrives at Telezart and look for Trelaina.
The Star Force defeats the last of the Comet Empire's resistance at Telezart and finally meets with the mysterious Trelaina.
The Star Force learns of the true nature and threat of the White Comet, Trelaina's dark past, and are ordered to return home to help fight the oncoming threat. But Venture may have other ideas...
The Argo prepares to leave Telezart, but will Venture choose to stay with Trelaina on her doomed planet?
Wildstar orders a warp to take the Argo to the Comet Empire. When the Argo reaches the coordinates, however, the Star Force discovers that the Comet Empire is headed to Earth, while they find themselves quickly surrounded by Gamilons, led by Desslok. Wildstar tries to convince Desslok not to attack, but Desslok sends his entire fleet after the Argo, heavily damaging the Argo's landing dock and surrounding the ship.
Although badly wounded and bleeding, Wildstar confronts Desslok on his ship. Desslok prepares for a duel, but Wildstar collapses from the loss of blood before he can fire. Having followed Wildstar, Nova rushes to his side, confessing her love for him and for the Earth. Realizing that Nova and Wildstar love Earth as much as he loves Gamilon, Desslok lowers his weapon, giving them a piece of advice as he leaves: the Star Force attacked Gamilon at its weakest point, from underneath. He suggests they attack the Comet Empire the same way.
As the Argo launches torpedoes against the Comet Empire, Zordar orders the Empire to be launched. The Argo pursues the Empire, positioning itself out of range of its guns, and maneuvers itself below the Empire. Sandor discovers the Empire's weak spot: an opening in the base from where the Empire's planes are being launched.
Zordar's space fortress launches an assault on the Argo, heavily damaging it and injuring several of its crew. As the Star Force watches helplessly, Zordar attacks the Earth. Meanwhile, Trelaina uses her life force to bring Mark Venture back to life.