Dr. Daniel Jackson and Dr. Rodney McKay have been forced to reactivate the Attero device, a machine designed thousands of years ago to annihilate the Wraith. In doing so, they discover the reason the device was ultimately abandoned by its Ancient creator. While destroying Wraith ships that attempt to travel through hyperspace, the weapon inadvertently causes active stargates to self-destruct.
Meanwhile, Todd and his troops continue to hold Woolsey, Keller, Ronan and the Daedalus crew captive, convinced that they are behind the resurrection of this deadly technology. Fearing that if Todd succeeds in destroying the device, Jackson and McKay will most certainly be killed in the process, Sheppard calls on some old allies to help him rescue his friends.