As the Ori invade the Jaffa planet Chulak, Vala and Daniel must deal with their leader: Vala's young daughter, rapidly aged by the Ori to serve their purposes.

SG-1 investigates a problem off-world and soon finds that they have become victims themselves: they cannot stay awake. Meanwhile, Vala Mal Doran undergoes an evaluation on Earth, hoping to join SG-1.

SG-1 visits Atlantis in the hopes of preventing the Ori from sending more ships through the Supergate, and to find a new lead on Merlin's anti-Ori weapon.

When Baal comes to Earth seeking help, Stargate Command must capture his clones and determine which one is the genuine article.

Teal'c discovers a world where people are being savagely attacked by an elusive creature, leading SG-1 to a stunning discovery about its potential origin.