Season 2 - Episodes 17-20:

2.17: Coup D'Etat -
Teyla and Ronin find a wanted list, and on it is a missing team member's name along with those of Sheppard and McKay. Sheppard and McKay's team is taken hostage by Genii accomplices. Their plan is to negotiate for Atlantis' Jumper ships. Now, Weir must negotiate with the Genii, before it's too late.

2.18: Michael -
Lt. Michael Kenmore learns that he was once a Wraith, and the Atlantis team has captured him and attempted to turn him into a human using the retrovirus that Dr. Beckett developed. The team must prevent Michael from rejoining the Wraith, or he will alert them to the existence of Atlantis.

2.19: Inferno -
The team is called upon to a distant village concerned by strong tremors. When McKay heads underground to investigate the problem, he finds that the tremors are being caused by a super-volcano. The leader agrees to evacuate his people. However, the team becomes stranded when the gate is destroyed by lava.

2.20: Allies -
Michael explains that the Wraith are engaged in a civil war, and he wants to turn the rival Wraiths human. In return, the Wraith promise a wealth of information about their technology. The partnership almost seems too good to be true, and as the team soon finds out, it was.