Complex sentence: U.S. Agent and several members of the now disbanded Mighty Avengers are called upon by Amadeus Cho to join the battle in Asgard and stop Norman Osborn's Thunderbolts from stealing Odin's spear from the Asgardian armory.
Split into simpler sentences: U.S. Agent and several members of the now disbanded Mighty Avengers are called upon by Amadeus Cho to join the battle in Asgard. They must stop Norman Osborn's Thunderbolts from stealing Odin's spear from the Asgardian armory.