Odyssey 5
The story follows six people on a routine flight of the space shuttle Odyssey, on August 7, 2007: four astronauts, a scientist, and a television news reporter. During the flight, the Earth rapidly dissolves into a fiery ball and implodes. Control of the Odyssey is momentarily lost, and one astronaut is killed. The remaining five crew members resign themselves to death, but an inorganic being called the Seeker rescues them. The Seeker tells them that fifty other worlds have been destroyed in the same way as Earth, and the Seeker has always arrived too late to observe it; this is the first time he has found survivors. He offers to send them five years into the past (to 2002, the year the series aired), so that they can prevent the disaster. He sends only their consciousnesses back, because physical time travel is impossible. The mission commander learns a codeword associated with the disaster: Leviathan.
The villains are a race of disembodied artificial intelligences known as "Sentients". These AIs are trying to learn about humanity through artificial humanoid robots called "Synthetics", which are nearly indistinguishable from humans. Another group of Synthetics are discovered to be from Mars. In the original timeline, a previous race of Synthetics created by humanity was destroyed by a secret US government agency. Whether the destruction of the Earth was retaliation for this act by the Sentients is never revealed.
While they search for the truth, the team must also revisit their pasts while retaining past knowledge of what is to come. Reporter Sarah Forbes tries to save her five-year-old son, who died of cancer in the original timeline. Her efforts in this direction alienate her husband, who leaves her and takes their son with him. Astronaut Angela Perry must deal with the knowledge that her father is a corrupt U.S. Senator whose malfeasance destroyed her family in the original timeline. Commander Chuck Taggart must try to keep his family together. His son, Neil, a computer technician on the Odyssey, must adjust to being seventeen again, when he was a poor student who hadn't yet discovered his talents. Pessimistic scientist Kurt Mendel believes they cannot change history and spends his time indulging every desire.
The series characters are not friends and frequently disagree; the humanity of the team is shown through arguments, jokes, and their attempts to maintain social lives and help the world with their limited knowledge of the future.
Many of the show's plotlines involve technologies like AI, nanotechnology and neuroimaging.
A recurring theme is that the actions of the group may hasten the cataclysm they are trying to avoid, or alter history in undesirable ways. A character who was supposed to live until 2007 dies in the first episode after helping the group. In one episode, Sarah and Angela protect a girl they know will be kidnapped. Although this prevents that individual's kidnapping, the kidnapper takes a different child. Kurt makes a large bet on a football game whose outcome is already known to him, but the pressure of knowing has a negative effect on a player instrumental in winning the game, and the team loses.
murder