Marvel's Avengers: The Extinction Key — Greg Keyes

Captain America, Iron Man, Thor, Black Widow, and the Hulk— Earth's Mightiest Heroes—have assembled to face world-class threats whenever and wherever they might appear. They are the Avengers. Yet some threats transcend the ages. Centuries ago, a never-before-seen group of heroes gathered as the Avengers of their ancient era to fight the Zodiac, foes who wielded unimaginable arcane energies channeled through a mysterious Key. The resulting battle devastated vast swaths of the planet. The Key was lost, and the Zodiac went into hiding, influencing world events from the shadows, waiting for the stars to align to usher in their return. When strange beings exhibiting the traits of the twelve astrological signs appear in the 21st century, the Avengers again answer the call to assemble. But when this modern team of heroes is forced to divide their efforts, each encounter leads to their opponents gaining strength. Once again, the hunt is on for the Extinction Key... and if the Avengers don't find it, our world will be lost.