The European country of Slorenia is dead. Every man, woman, and child eliminated with the cold precision of a machine. And out of the flaming remnants of this tiny Baltic state comes a message from its murderer: Mankind's days are numbered because Ultron has returned! He - or it - is one of the Avengers' oldest, most implacable foes, menacing humanity countless times. But never before has Ultron been this dangerous, this deadly. Now, he stands on the brink of committing global genocide, and rebuilding Earth in his own robotic images. Our only hope is a desperate U.N. strike on Slorenia, led by the Avengers themselves. But will it be in time? Will the strength and courage of Earth's Mightiest Heroes be enough in the face of such overwhelming evil? For the sake of the world, it will have to be! Plus: When you're an Avenger, you're one of Earth's Mightiest Heroes - the first line of defense against the dangers no conventional foe could halt, the threats no ordinary man could withstand. Threats including Dominex, Lord Templar, Pagan, and the Thunderbolts! Collects Avengers 12-22, No. No. 0 and Annual 1999.