MCU Theory: Could Captain Marvel's Missing Skrull Be A Hidden Avenger?
3. The Small Scale Secret Invasion
What we definitely know is that there's a Skrull left on Earth. What isn't clear at the moment is why that might be the case. If Talos wants to reunite all of his people, why would he be so careless? Well, actually, Talos' plan has two strands. It's not just about reunification, it's also about finding a new home.
The Skrull home planet Skrullos was destroyed by the Kree as part of their bloody war and the Skrull were scattered across the galaxy as they sought refuge from the murderous Kree who sought to exterminate them. They were driven underground in fear of ethnic cleansing and had no opportunity to settle anywhere. Some hid on distant worlds, some roamed the universe like Talos as a military unit and some were hidden by Mar-Vell/Dr Lawson. As long as they were still being hunted and had little hope, they could seek no home.
That all changes with the alliance between Captain Marvel and Talos. Not only does it allow Talos to find his family and the other survivors, but even more importantly, it equips the Skrulls with a God-like champion to protect them. They effectively turn the Kree's most valuable weapon against them (just as they previously turned one of their most important scientists against them in Mar-Vell) and disprove the idea that the Kree are an invulnerable enemy.
In a short space of time, Marvel defeats Yon-Rogg and his Kree and then terrifies the Accusers to such an extent that they turn on their heels and run away. Sure, Ronan offers a parting shot that he'll be back, but he won't do anything meaningful. We know that his future includes an even bigger defeat at the hands of the Nova Corps - or at least a symbolic defeat for everything he represents in the shape of the peace treaty between his people and Xandar. That treaty renders him redundant: he was bred for war and the idea of peace after centuries of conflict disgusts him. And importantly, by the time that happens, he's turned his attention away from his vengeance on Captain Marvel.
Why mention that? Well because it's an important shift in the status of the Skrulls. They go from being the singular concern for the Accusers to being inconsequential by 2014. That's an incredible shift in less than two decades and it's all down to Captain Marvel being their pocket messiah.
Marvel represents hope for the Skrull people and she represents a chance for home. With the tide in the relentless pursuit of the Kree turned (but not completely arrested of course because the Kree remain active and will recoup as a wounded animal, they can start to think about the second part of Talos' plan. They can start to look for a home.
At the same time, Talos still needs to search the universe for his scattered people, but he has one eye on the endgame. So why wouldn't he leave one of his most trusted men to scope out Earth as a possible sanctuary in the long-term? Could that be what the missing Skrull is doing on Earth? Testing the waters for when Talos has completed his mission and united his people?