The crew members of the Odyssey 5 space shuttle witness the explosion of Earth from an orbit far above. They are rescued by The Seeker and given the chance to save Earth. The Seeker sends them 5 years into the past to attempt to avert the destruction of the planet.

The Odyssey 5 team tries to locate Professor Naran Chandra, an artificial life researcher who in the original timeline will commit suicide at a lecture 8 days from now, right in front of Kurt. Examining the files on Chandra's computer, they find that Chandra discovered a computer lifeform loose on the Internet that apparently evolved on its own from experiments in Chandra's lab and has now become "Sentient". Meanwhile, noting how mature and responsible his behavior has suddenly become, Neil's girlfriend Holly talks about taking their relationship to the next level. Sarah and Angela's investigation of the patients given "gene therapy" by Dr. Barantz leads them to discover some living tissue that appears to have been bio-manufactured in a chemical vat. Then, when they finally meet the frightened Dr. Chandra, the team discovers that one of his students is actually an inhuman creature made from this same nearly-indestructible tissue.

NASA's Project Bright-Sky is accelerated due to Ed Scriven's death and, knowing that a next-generation version of the Bright Sky satellite is what Odyssey 5 was launching on the day Earth was destroyed, Taggart determines that he must put his career on the line to sabotage the deployment of the current version. Neil realizes he's falling in love again with his old high school girlfriend, Holly. Sarah and Angela use their knowledge of the future to try to stop the kidnapping and murder of a young girl, which was front-page news in the original timeline, only to find that their actions have changed the future unpredictably. Mendel, determining that an organism comprised of the mysterious artificial tissue would be cold-blooded, assembles a thermal imaging system that will distinguish humans from the "Synthetics".

In his continuing unsuccessful quest to make a huge amount of money from his knowledge of the future, Kurt marries a young woman who is destined to be a big star in the music world 5 years hence, but whose music is currently unpopular. Then, one by one, the Odyssey 5 members start losing their future memories. In desperation, Taggart and Mendel consult a theoretical physicist who is lecturing at a local science fiction convention, pretending that they need help with the science in a time-travel novel they are working on. But all they are able to determine is that each victim has the urge to type a bunch of weird symbols on a computer screen just before losing their memories of the next 5 years. Finally, Mendel is the lone survivor. As if stuggling with his new marriage wasn't trouble enough, if his memory goes before he can figure out what is going on, there will be no one left to save the earth from ultimate destruction.

When a top prosthetics researcher is found dead, Neil receives an anonymous e-mail telling him that the man was murdered by the "Synthetics" whose existence the Odyssey 5 group has discovered, which it says are the physical manifestations of Dr. Chandra's "Sentients". It claims that they are now after the researcher's six-year-old niece Stevie, all because of a ""cybiotic interface"" he was working on which would allow computer technology to control organic systems. Visitng Stevie's teacher, they find out that she is deaf and received a cochlear implant, which her uncle had been tinkering with. Eventually, the team locates Stevie and finds out that her implant allows her brain to control a swarm of insects that have been fitted with cybiotic interface chips. But mysterious figures who may be Synthetics have relentlessly tracked Stevie to Kurt's place.

A mysterious being, who is not bound by time, notes that the Odyssey crew have jumped out of their proper time and comes to investigate them. It probes their minds and forces them to re-visit the personal choices they made in the most important moments of their past lives.

Neil's friends at school are taking a new drug called "Rapture", which appears to boost their intelligence and may even promote telepathy and telekinesis. Neil finds out that his friend Deckard got the formula for the drug from a web site, but in his attempt to get a sample for analysis he is forced to take the drug. Meanwhile, Taggart's new boss Cynthia Hodge suggests that he had something to do with sabotaging the last space mission, but appears to be happy that the mission failure has hastened the day when manned space flights will be replaced by totally robotic ones. A retired astronaut, Leyton Scott, tells Taggart that a group called "the Cadre" have been trying for the last 20 years to get rid of manned space flight. But then Leyton reveals that he is dying from "Moon Sickness", a strange disease that strikes only Apollo astronauts, which may have something to do with their having brought more than just rocks back with them from the Moon. Because of Angela's apparent mental br

Taggart, Mendel and Sarah visit a privately operated Maximum Security Prison hoping to find a clue to locating a powerful, dangerous Sentient. They ultimately find themselves trapped within a Synthetic and it's a race to the death.

Marc faces expulsion from the Astronaut Training program. Paul takes Sarah to court because of her apparently irrational obsession that their son will get cancer. Taggart suffers from the effects of a Sentient-designed virus.

Neil's friendly emails with a mystery woman come back to haunt him when "she" turns out to be a Sentient who is growing increasingly obsessed with him and curious about Odyssey 5. "Kit-10" wants to know the secret of the Odyssey 5 mission -- but just how far will she go to get what she wants?

The residents of a small town and a select group of scientists (including Mendel) are brainwashed into believing "The Lord" has specially chosen them to construct a passageway designed to bring "Him" to Earth. Taggart and Neil must reach Mendel, before it's too late.

The O-5 team is approached by "Harry Mudd" -- a Sentient in a Synthetic body. He warns them of the imminent destruction of the world by an insane Sentient and reminds them about what's important in life.

The Odyssey crew scramble to save the life of Angela's father, Senator Perry, when he's threatened by a terrifying new breed of Synthetic. Paige deals with her emotions after learning the truth about the Odyssey mission.

With the still-grieving Chuck having taken off on a road trip, the rest of the crew have to deal with the synthetic that Kurt has created.

When Taggart wakes up in a hospital with Paige beside him, he begins to believe that the destruction of the world may have been a dream. What he doesn't know is that it is all a ruse by Dr. Bertran, who is trying to stall his activities long enough to download information from his brain.

The team uncovers a Sentient plot to use elementary school students in the creation of a Doomsday weapon.

Angela is haunted by the apparent ghost of a pilot who disappeared two years ago.

Chuck and the rest of Odyssey 5 remember a riot in a Houston suburb, and the date is approaching. People in the town are becoming angry, even to the point of killing loved ones - and afterward, they can't remember why. The rush is on to discover what's causing this rage, and how to avert the riot.

During the surveillance of a suspected Synthetic front, Angela and Kurt engage in a firefight which leaves Kurt in the hospital and Angela abducted by the Synthetics. Following a tip from his old friend and Menthor, Leyton Scott, Chuck learns of a rock, brought back from the moon, that is the link between the Cadre and The Sentients.