The adventures of the Ultimates continue following the events of Ultimatum. When the once laughable "superteam" the Defenders suddenly acquire actual superpowers, they attack the Ultimates and steal Mjolnir from their former teammate, Valkyrie. As the team retrieves the weapon, they get caught up in an Asgardian power play that may return their fallen comrade to their ranks.
Ultimate Comics: New Ultimates - Thor Reborn
Ultimate Comics: New Ultimates #1-5