On Atlantis, Teyla is asleep when she is attacked by a Wraith . . . who mysteriously disappears when she wakes up. She goes to Sheppard's quarters and finds a desiccated corpse and the Wraith . . . and she wakes up again.
Weir confirms they have less than a week before the Wraith arrive and looks for various options. There is disagreement over whether to stay and fight. Later, Dr. Heightmeyer, a psychologist, approaches Teyla, who is unhappy with Sheppard who sent her. Sheppard leaves her behind as her and Ford check out their Alpha site.
Later, taking a nap, Teyla decides to meet with Heightmeyer, who explores Teyla's ability to sense the Wraith. Under some careful prodding, Teyla reveals she saw herself in the dream as the Wraith standing over herself. Heightmeyer suspects there is some connection to the Wraith, but Beckett can't turn up anything in Teyla's DNA. Teyla visits her old friend Charan, who reveals a secret about Teyla – her father was one of a number of people taken by the Wraith but came back . . . changed. Teyla convinces Sheppard and Weir to send an expedition to the planet where her father was taken.
On the planet McKay finds an energy source and Teyla is able to pass through a solid wall and enter a chamber that looks like the interior of a Wraith ship. It's a secret Wraith laboratory and McKay brings some files back to Atlantis that may hold the secret to the Wraith experiments on humans. Under prodding by Heightmeyer, Teyla has more feelings of being a Wraith.
While the scientists try to activate the command chair, Beckett determines that Teyla has Wraith DNA, as a result of an unauthorized experiment on her father and the others. Beckett determines that the Ancients inadvertently created the Wraith by combining human and insect DNA. Teyla is concerned that the others may fear her. McKay determines the Wraiths stopped the experiment because it was allowing their subjects to tap into the Wraiths' telepathic network. Heightmeyer uses hypnosis to unlock the potential in Teyla, who experiences a Wraith feeding on a human.
Weir is reluctant to continue experimenting with Teyla, but Teyla insists and the next time manages to access one of the approaching hive ships. A Wraith briefly speaks through her but they manage to break the "connection." The team at the Alpha site is forced to return when the Wraith attack and "tag" the planet – the place is useless to them as an evacuation point. Weir and the others begin to suspect the Wraiths learned the location through Teyla – the telepathic link may be two-way. Teyla warns that the Wraith want something, and that due to their premature awakening there isn't enough food to support their mass numbers.
Teyla insists on making another attempt but this time they're unable to break the connection and the Wraith go berserk through her. They manage to stun Teyla and break the connection, but later she reveals that she now knows why they're coming to Atlantis – they need a new feeding ground and plan to go to . . . Earth.