Using Mjolnir, Thor's enchanted mallet, the Incredible Hulk flies through the Ice Giants hitting and breaking them hard until he goes up to a mountain top where the God of Thunder is waiting. There we learn that Hulk wasn't really "worth it" to hold the hammer, but it was Thor who commanded his weapon to move, carrying the Jade Giant with it.
Ice Giants find the portal back to Banner's S.H.I.E.L.D. lab, but Maria Hill and Agent Coulson repel the invasion. The portal has been damaged. Scientist Melinda Leucenstern (from Banner's team) brings it back on but it connects to different places and times. Banner and his group are now trapped in Jotunheim.
Earlier, scientist Randall Jessup (another team member) was captured by the enemy, and one Ice Giant took on his form to infiltrate the Earthlings secretly.
Finally, scientist Patricia Wolman reveals Bruce Banner that she would like to commit suicide, and chose the Hulk to kill her.