In the year 2160, people live in a giant, fusion-powered cities. Also present are the Cephians: plantlike aliens who have come to Earth to determine humanity's readiness for joining their galactic community. Though friendly, they've been here for 40 years, and humankind's trust and patience are wearing thin, at times violently so.
Dr. Shana Savarino, an eminent astrobiologist, feels otherwise. A quiet, sensitive but sultry stunner, she has issues with people, who have objectified and played her whole life. As an act of rebellion, she scarred her face when she was younger. There are some humans, colleagues mostly, whom she does like, but overall she prefers the company of the Cephians, especially one who is her closest friend.
Meanwhile, geologists in Mexico, using underground nuclear explosives to study a prehistoric crater, discover a deeply buried, unknown artifact. This artifact, a sentient entity, awakens and thinks it's being attacked. Shana and her team are alerted, as are the Cephians, and when Earth's global defenses and Cephian forces investigate, the artifact escapes the area, later assaulting the New York megatropolis as a rampaging dragon. This exacerbates tensions worldwide between human factions: those who continue to trust the aliens, and those who -- despite Cephian help in fighting it -- see the beast as a deceptive, first-strike Cephian weapon for dominating Earth.
All joint human/Cephian efforts to stop the dragon fail as it strafes the planet, obliterating cities across continents. Getting near it to study it, Shana is nearly killed, only to awaken in a virtual realm where she meets the intelligence inside the dragon, called a Sequencer. She learns that this Sequencer is Earth's protector against future aggression, having been placed inside the planet after the dinosaurs had been attacked in an ancient galactic war. She realizes the Sequencer is really a caring, noble being, but it had been damaged in that war, is now unable to cease its attacks on Earth, and so is internally suffering. Shana tries to help the Sequencer, and it bonds with her but only her, as it keeps killing millions. She gambles that the only way to convince the Sequencer that killing everyone else is wrong is by offering her life instead. This was still her home, her kind. In renewed solidarity with the human race, Shana deletes her symbol of rebellion, that scar, from her face.
The Sequencer, inspired by her sacrificial willingness, seeks to end its own life by plunging into the sun. As it yields to its fate, the sun's fire cures it, and the Sequencer returns to its original, simpler form. It tells Shana it wants to find its creators to heal the Earth. But being left somewhat brain-damaged, the Sequencer needs guidance and asks Shana to come with it. Given the opportunity to explore the universe with this noble creation, Shana accepts.
In the months to follow, the human race continues to recover with Cephian aid. In recognition of its valor during the Sequencer Event, humanity is awarded galactic membership, and a bright, unprecedented future beckons. As for Shana Savarino, for her part in saving the world: she is honored in absentia, quietly, the way she would have preferred.
