A group of trainees and their leader, veteran gate traveller Gus Bonner, must help an alien named Draga, who is being pursued by both alien forces and bounty hunters from Earth, get back to her homeworld.

The team stay on a jungle planet, cut off by Nephestis who has framed Gus as a traitor. The local Thorn aliens are dying of a disease which Gus believes he left there on a previous expedition. The others choose to head out with the Ancient chrysalis but are ambushed by the Tlak'khan but escape...as the chrysalis hatches and the winged Ancient escapes. The Tlak'khan leader De'kyll takes the Thorn village hostage and Bonner surrenders but the Ancient intervenes and the cadets take them prisoner (except De'kyll escapes). The Ancient learns English through Seattle and asks the team for help, and after being named Draga. Draga heals the ailing Thorn but knows nothing about the Stargates and remains with the team.

After escaping the Tlak'khan on a jungle world thanks to Harrison's flying skills (sort of), the team arrives on a sulphur-covered planet and bat-like inhabitants, the Har'un. With his jetpack damaged Harrison accepts an invitation to fly with the locals but doesn't do so well. Determined, Harrison keeps trying but is the only one in the group who can't manage. The planet is polluted due to the Tlak'khan's efforts and they send a team to attack - Harrison has to mount up to warn the others and manages to get the hang of it. the Tlak'khan refuse to learn from their mistakes and fall victim to the Har'un's gas bombs.