"Secret Invasion" is a Marvel Comics storyline that focuses on the infiltration of Earth by the Skrulls, a shape-shifting alien race. The plot reveals that many superheroes and key figures have been replaced by Skrull impostors, leading to a crisis of trust among the Avengers and other heroes. The story explores themes of deception and identity, as characters must determine who is real and who is a Skrull. It highlights the challenges of loyalty and the consequences of betrayal, ultimately questioning the nature of heroism in a world where anyone could be an enemy.