When Teyla and Dr Keller visit Teyla's home world, all is not well. The Athosian village is deserted and Teyla, as it turns out, wrongly suspects a warrior race, currently on the planet, of killing them all. Dr Keller has never been off world and finds the whole experience terrifying.
By the end of the episode, we are no wiser as to what has happened to the Athosians, but more importantly, Dr Keller has something of a medical nature to tell Teyla. The nature of this is not revealed as the episode concludes.