A Necessary Evil

When Sheppard's team encounters a culture with phase shift technology that keeps their entire population invisible - and immaterial to the outside world, it looks like Atlantis might have found the perfect protection from the Wraith.

Eager to make a trade for the technology, Dr Weir embarks on a diplomatic mission to negoitate with the people of Lannavulin, but once there, it becomes apparent that not everyone is happy with the planet's status quo.