As Avengers: Infinity War hurtles toward its April debut, plenty of questions still loom over the Marvel Studios ensemble film. However, one of those may have been answered by context clues provided by the epic final trailer: how, exactly, Bruce Banner ends in Doctor Strange's New York Sanctorum. Surprisingly, Loki may (literally) hold the key.
Let's look at where we last saw our heroes: Loki and Hulk joined the god of thunder in Thor: Ragnarok, traveling separate paths but ending up in the same place -- aboard the Sakaaran ship filled with Asgardian refugees, on a course for Earth.
The Hulk's narrative in that film was pretty linear. He, and, by extension, Banner, formed a new bond with Thor, which led him to join the thunder on his quest to save Asgard. During the massive third-act battle, Banner even made a sacrifice to help Thor's people by transforming into the Hulk, despite concerns that may not be able to return to his human form. Thus, he helped to rescue the Asgardians before their home world blew up, and then joined them on their journey to Earth in search of safe haven.
Loki is where it gets interesting. As Thor, The Avengers and Thor: The Dark World demonstrated in spades, the god of mischief has a rather fluid sense of morality. The opportunistic Asgardian, generally out for himself, has a tendency to sacrifice other people's lives if they get in the way of his goal. However, in Thor: Ragnarok, a heart to heart with his brother seemed to change him. When he had an opportunity to escape Sakaar and leave his past behind, he instead returned to Asgard to help Thor and their people. The conclusion of Ragnarok heavily implied Loki had turned a new chapter and planned to forge a more heroic life.
Of course, old habits die hard, and Loki didn't leave Asgard without taking a little souvenir from Odin's treasury. On his way to place the Crown of Surtur into the Eternal Flame, which kick-started Asgard's destruction and ended Hela's reign, he paused when he saw the Tesseract, which encases the Space Stone. That implied he absconded with it from Asgard, which was later confirmed by the first Infinity War trailer. As such, Loki is in possession of the Space Stone at the end of Thor: Ragnarok.
It should be no surprise, then, that Thanos tracks down the Asgardian refugees in his quest to assemble all six Infinity Stones, as strongly suggested by the mid-credits scene of Thor: Ragnarok. As both trailers for Infinity War suggest, that encounter somewhere in deep space doesn't end well for those aboard the Sakaaran vessel. Indeed, the teaser trailer shows someone stepping among what appear to be the bodies of Asgardians, before Loki reveals the Space Stone is in his possession.
However, as we see in the Infinity War trailer released on Friday, Loki's former boss isn't exactly pleased to see him. One shot reveals Loki surrounded by the Black Order, with Proxima Midnigh pointing her spear at his head. That certainly implies the Asgardian trickster is their prisoner, not an ally, despite working with Thanos in The Avengers. Noticeably, Loki doesn't seem to have the Space Stone in that scene.
Thanos has good reason to be mad at Loki. After all, he gave Loki the Mind Stone, only for Loki to lose it to the Avengers. What's worse, Loki ultimately got what he wanted: to rule Asgard. And Thanos received nothing in return. But there may be more to this scene than an old grudge.