Vengeance

"Vengeance" is the title of the nineteenth episode of the third season of Stargate Atlantis.

Summary
Dr. Weir reports that the Taranians haven't contacted Atlantis in over two months. John Sheppard's team is sent to look for them. On the planet they discover it appears as though the whole settlement has been abandoned.

Detecting a life sign below them, the team searches an underground complex made by the people who lived there before the Taranians. There they are faced with a large creature which has similarities with the Iratus bug, after finding a room full of dead Taranians, an Iratus Bug in a jar full of liquid and a large cocoon/pod in an empty room.

After a scheduled check in, and before the team comes into contact with the life sign, Dr. Weir sends them a Marine contingent to help them deal with the creature, but soon after they arrive they are abducted by a Wraith dart.

After Sheppard's team has little luck with destroying the creature (Ronon only manages to cut off its arm) and realizes they've lost contact with the Marines, they try to return to Atlantis, only to find that the control crystals have been removed from the DHD, disabling the gate. Returning to the complex they discover that Michael Kenmore, after being rejected by the Wraith began experimenting with the bug and created these creatures to take over the galaxy. They soon discover that he has hundreds of those creatures on that planet and this is not the only planet he is breeding them.

While McKay and Teyla stay in Michaels lab where McKay tries to figure out what Michael was doing and how many creatures are on the planet, Sheppard and Ronon use the air vents to get to the surface and locate the control crystals. Unable to find the control crystals and with the creatures on their tail, they quickly find Michael's Wraith dart. Sheppard is able to fly it and then beam Ronan, Teyla, and McKay on it and then use its DHD to dial out.

Daedalus is redirected to go and nuke the planet but when they arrive there they find that the whole place is wiped clean with no sign of Michael or the creatures.

At the very end of the episode, Dr. Weir explains to Teyla that it was their fault the Taranians were killed, as the Wraith discovered their location after they hacked the Atlantis Database during the episode Allies. Dr. Weir also mentions that according to what McKay was able to decipher from Michael's device, there are at least three other planets where Michael was conducting his experiment and there are hundreds of beasts out there.