Plot summary
Todd informs Atlantis that a group of Wraith have in their possession several ZPMs which they plan to use to power a new super Wraith Hive. He also advises Woolsey that they should immediately destroy it. But when the team reaches the hive, it does significant damage to the Daedalus and jumps into hyperspace. The team then finds out that the ship has received the signal sent from alternate Earth in "Vegas" and is heading to Earth. The hive shrugs off all efforts to destroy it, including an attack by Atlantis itself, but at the last minute, Sheppard destroys the ship with a nuclear weapon and saves Earth. Atlantis is forced to land on Earth due to lack of power.
Credits
Adapted from Wikipedia contributors, Stargate Atlantis season 5. HTML formatting and reference markers removed.