For his entry in the big “Earth is a prison planet” story, Cap fights some aliens and gets help from a dude who calls himself “Sarron.” Sarron says he can open a portal to evict the bad aliens, but he needs Cap’s shield to do it and they have to do it at the Statue of Liberty.
Of course it’s a trap, and Sarron is really Mercurio, who is trying to use Cap’s shield for his own escape plan, having been sentenced to Earth-based imprisonment.
They fight and Mercurio either dies or actually succeeds in his portal plan. It’s not clear which.