"No major construction for 'The Seer,' but we will marry some of the exterior scenes from this episode to the 'This Mortal Coil' shoot. James and Tom also pitch out how they'd like to pull off the 'horrific reveal' at script's end. I love it!"
Executive producer Joseph Mallozzi, in a message at his blog

The city of Atlantis is visited by a man with extraordinary prophetic abilities, and who apparently has the ability to share these shocking visions with others. The gentle man is named Davos, and he is accompanied by a woman named Linara.

But Davos is quite ill. He believes that he is dying, but before he passes on he will share what he knows with those who now live in Atlantis, the city of the Ancestors. There are Wraith hive ships coming.

When Teyla goes to speak with Davos, he already knows that she came to his planet seeking to learn the fate of her people, the Athosians. It is not clear where they have gone or what has happened to them, but Davos can assure Teyla that they are alive -- though they are "shrouded in darkness."

And Davos knows more than this. He also knows that Teyla is pregnant.

She is stunned that he knows, and confesses that she has not told anyone on Atlantis yet.

Meanwhile, Rodney McKay is working on a major problem, which he describes to Colonel Carter and Richard Woolsey. The Wraith have found a way to shut down or in some way disable the Replicators, but McKay inadvertently managed to turn them on again. With help from a certain Wraith they have met, he hopes that they can stop them once again.
GateWorld news report