Col. Jack O'Neill retired from the military a year ago. Just before he left the service, he led an expedition through the stargate, an ancient portal that allows instantaneous travel to other galaxies. He is called back to duty by Gen. Hammond when a group of aliens emerge from the stargate, kill the soldiers guarding it, and kidnap a female guard. After seeing the aftermath of the alien attack and the strange bodies they left behind, O'Neill confesses that he defied the order to destroy Abydos, the world he visited via the stargate. He reveals that Dr. Daniel Jackson, the scientist who was thought to have died on that mission, is alive and living on Abydos. It is also clear that these aliens are not from Abydos. O'Neill is reunited with his old comrades Kawalsky and Ferretti and joined by Capt. Samantha Carter, an astrophysicist. SG-1 returns through the Stargate to Abydos. They discover that Jackson has taken an Abydonian wife, the beautiful Sha're, and that Skaara, the young Abydonian boy whom O'Neill cherishes like a son, has grown into a fine young man. They also see Jackson's latest discovery: a giant cartouche covered in hieroglyphics that seems to be a map of many stargates throughout the galaxy. As they marvel, however, the aliens, led by the handsome but evil Apophis, are making use of a similar map. They emerge from the Stargate on Abydos, and, after a brief battle, kidnap Sha're and Skaara. Ferretti, who was wounded in the firefight with the aliens, has seen the hieroglyphic code that indicates the aliens' destination. O'Neill and Jackson are determined to follow the aliens and to save their loved ones. With a troop of soldiers from Earth in tow, they track the aliens to the planet Chulak. There they discover that Sha're is now Apophis' queen; her body has been taken over by a hideous snake-like creature, one of a species known as the Goa'uld, who rule this planet and collect life-forms from around the galaxy to use as hosts. Jackson and O'Neill know that they can't save Sha're — but can they save themselves and Skaara before they're killed by the Goa'uld's guards and before Gen. Hammond sends a nuclear weapon through the stargate to destroy the planet?