D'Argo and Stark try to heal John, left with his head open on an operating table, while Scorpius attempts to avoid discovery. Zhaan makes a great personal sacrifice, while Jothee and Chiana commit an indiscretion.
Moya's crew must escape the aliens and the deadly wormhole when they discover that the ship's dire situation was caused by sabotage. One of the crew makes a sacrifice to save the rest.
D'Argo, John, Chiana and Jool are forced to land on an abandoned Leviathan, and are preyed upon by a brain-sucking psychopath who has taken over the ship and turned its crew into flesh-eating zombies. Moya finds Talyn adrift, with Crais unconscious on board.
The crew must travel to a planet to obtain medicine for Talyn, and learn that a Peacekeeper Retrieval Squad is hunting him. Aeryn learns the truth about her past.
A giant Budong swallows Talyn, and tempers flare between Crichton, Crais and Aeryn as they attempt to find a means of escape. Aeryn makes a decision that could change her life forever.
The crew must discover which of them has been possessed by a parasitic Energy Rider, before the being that has come to find it kills them all. Meanwhile, Scorpius finds a deadly problem with his wormhole research.
Aeryn must face her mother when the Peacekeeper Retrieval Squad catches up with them. Crichton discovers that Talyn isn't the only one the Peacekeepers are after.
When Scorpius runs into trouble decoding the wormhole technology taken from Crichton's brain, he appeals to John for an alliance -- offering to reveal his own shrouded past.
When Moya's crew visits a pleasure planet for shore leave, Crichton and D'Argo are taken advantage of -- and learn that Jool and Chiana have been captured to have their essence harvested.
Crichton is reunited with the Ancients when an old acquaintance unlocks the secret of wormhole technology -- threatening the entire galaxy should the Scarrans acquire it. Talyn and Crais are blinded by a solar flare, while John attempts to force Scorpius' neural clone from his mind.
Crichton and Aeryn race to construct a powerful weapon to fight an approaching Scarran Dreadnaught, poised to claim powerful wormhole technology that could help them conquer the galaxy. Crais and Stark deal with a Scarran who boards Talyn and tries to take command.
An accident puts Crichton in a coma, where he uses his imagination to fight for his life. D'Argo tries to stop an alien ship from self-destructing, and taking Moya with it.
Aeryn tries to contact her deceased father on a planet fraught with mystics and frauds, but encounters an all-too familiar face. Crais is forced to make a shocking confession.
Crichton and the crew board Scorpius' command carrier, launching a secret plot to sabotage his wormhole research. But a Peacekeeper commandant works to destroy their alliance and sign a peace treaty with the Scarrans.
Crichton is forced to go to extreme measures to destroy the Peacekeepers' wormhole research, and is betrayed to Scorpius. Two comrades must make the ultimate sacrifice.
The crew encounters a hostile Leviathan while trying to lay their friend to rest. Crichton and Aeryn must decide the fate of their love as the rest of the crew prepares to go their separate ways.
