SG-1 is accused of stealing an important weather-controlling device, sending a primative planet into chaos. The team discovers that Earth's second Stargate is being misused.

SG-1 discovers the village of Camelot on an alien world, and must face Merlin's security system when they go in search of an Ancient weapon. Elsewhere, Earth and its allies assemble a fleet when a working Ori Supergate is discovered.

Daniel and Vala travel to Atlantis in search of Merlin's anti-Ori weapon, while Sam, and Mitchell join forces with Dr. McKay to lock out the Ori supergate.

When the team finds Merlin himself, they must help him complete the Sangraal weapon before Adria and her Ori forces can track them down.