CourtesyTrefflin
When Loki let the Jotuns into Asgard, he didn't think the truth of his actions would ever come out. Until they do. After Thor falls into the void, Loki doesn't see him again until he's sent to Earth to stop his brother's attack. An alien invasion is the last of things Steve expected to draw him back into the fight, but with an old threat from his past returning, he doesn't have much choice.