Teyla awakens to a horrifying sight: A Wraith standing over her bed, his hand on her chest sucking the life out of her. ... It's only a nightmare. She goes to Maj. Sheppard's quarters ... to find his flesh rotted away, the life drained out of him and a Wraith waiting for her. She is still in the dream - one of many Teyla has suffered lately as the Wraith close in on Atlantis.
With the Wraith less than a week away, Sgt. Bates has the Alpha site ready for evacuation and Sheppard is on his way to inspect it. Sheppard suggests that Teyla, who has confided in him about her dreams and that she has been badly distracted of late, see Atlantis' psychologist, Dr. Kate Heightmeyer.
Later, Teyla tells Dr. Heightmeyer how she and a few others have been able, since childhood, to sense the approach of the Wraith. Most frightening to her is that, in one of her dreams, she is a Wraith.
On the mainland, Teyla consults Charin, one of her people's elders, who tells her of a planet long ago that was culled by the Wraith. On several occasions, the Taken had come back. The Taken were feared by the other Athosians. They heard voices; some became violent, even murderers. The other Athosians killed most of the Taken and ostracized others. It is believed that the Taken who survived in exile passed on "the gift" of sensing the Wraith's approach. Teyla has the stargate address to this planet, which might hold answers for her - and possibly a way to defeat the Wraith.
Teyla, Sheppard and Lt. Ford 'gate to the planet. It seems abandoned. Then Teyla steps through a solid rock wall. It is the entrance to a secret Wraith laboratory that only Teyla could access.
Later, back on Atlantis, Dr. McKay downloads data from a recorder that Teyla found in the Wraith lab. Dr. Weir and Dr. Beckett scour the data and find something disturbing. It appears that the Wraith evolved after the Ancients arrived in the Pegasus galaxy: The Wraith language is a dialect of Ancient. The log tells of a Wraith that experimented on Teyla's ancestors to make them more genetically compatible with the Wraith species and easier to feed upon. As a result, Teyla has a small amount of Wraith DNA in her genetic code.
Upon further examination of the Wraith scientist's log, Weir discovers why the other Wraith forbade his experiments and sent him into hiding. The fusion of Wraith DNA with that of humans enabled the humans to develop a psychic link with the Wraith, one that allows the humans not only to predict their coming but also to read Wraith minds.
Teyla allows Dr. Heightmeyer to put her under hypnosis, under Dr. Beckett's supervision, in the hope that she can tap into this Wraith psychic network and learn the enemy's plans.
The first attempt is traumatic: Teyla feels like she is a Wraith on one of the Hive ships; then she feels what it's like for a Wraith to feed on a human. She is snapped out of hypnosis by Dr. Beckett but insists on trying again. The second time, she is in a Wraith control room. Then she becomes possessed by a Wraith who tells Weir and company that they are all going to die. Again, she is rescued from the trance.
Incoming wormhole! Bates and team come in hot. The Alpha site has been compromised by the Wraith. The only way they could know about the site's location is through Teyla's connection with them.
Teyla insists on trying again, because she saw a holographic map that could yield vital intel. This time, during the hypnosis session, Teyla becomes violent, throwing around Sheppard, Beckett and Ford like rag dolls. Bates stuns her with a Wraith weapon.
Later Teyla reveals what she saw during the experience: The Wraith's plan is not just to take over Atlantis. From the Wraith Queen's interrogation of Col. Sumner during their first encounter, they have learned of a new and more plentiful feeding ground, one they can reach only via Atlantis: Earth.