The story is basically "Die Hard" in the Avengers mansion. Zemo and the Masters of Evil monitor the activities of the Avengers, and overrun the mansion at a moment it was empty. They easily subdue most of the Avengers that enter it, unaware of the problem, and eventually flee when the remaining Avengers are aided by Thor.
Under Siege provides examples of:
- All Your Base Are Belong to Us: One of the most famous instances in comics, a large group of supervillains, the Masters of Evil, take over the Avengers Mansion and turn its weapons, comms, and other systems against the heroes.
- Berserk Button: Reminding Hercules that the Wasp is the boss that gives him orders is not exactly a good idea.
- The Chains of Commanding: Discussed by Wasp. When grieving over her team-mates being decommissioned and Avengers Mansion being occupied, Black Knight consoles her but Wasp points out that it's her responsibility that the Masters of Evil took over since it was her watch. She didn't plan out the defenses or anticipate the situation they were currently in and that makes it her responsibility as team leader.
- Chekhov's Gun: "And, in another news, supervillain Moonstone has escaped from prison. Back to studios". It shouldn't surprise anyone that she shows up later.
- David Versus Goliath: Ant-Man & the Wasp vs. the Absorbing Man and Titania. It can hardly be more unfair than that.
- "Die Hard" on an X: The basic premise is "'Die Hard' in the Avengers mansion"
- George Lucas Altered Version: Birrah asked Namor for help to liberate Atlantis, and he left with him. All the siege goes on, with Namor absent...in the TPB, at least. Actually, Namor called the Avengers at the end of #271 and they helped him in #272, all which were removed from the TPB to keep the story more focused.
- I Reject Your Reality: Helmut Zemo is convinced he's avenging his father's death and family dishonor despite the Avengers and Captain America telling him that his father was a Nazi war criminal, a culprit of its atrocities, that he got himself killed, and it was him who brought all the difficulties on himself and his family as consequences of his actions. Helmut is too insane and evil to accept this of course.
- Kick the Dog:
- Zemo does not really gain anything from tearing Captain America's photo of his mom. It's just because he's evil.
- Mr. Hyde also decides to savagely pummel Jarvis while the Black Knight and Captain America are Forced to Watch.
- Mirrored Confrontation Shot: Avengers #271: The Black Knight, Wasp and Paladin vs. the Grey Gargoyle, Yellowjacket (Rita Demara) and Screaming Mimi.
- Not So Stoic: Zemo tore the only photo of Captain America's mother up in front of his face. Cap stayed serious and collected, and only said "I will remember this, Zemo". But that was then, when there were people at risk and lives at stake. Once the battle was over, Cap was crying with the pieces of the photo.
- Reality Ensues: What happens when Hercules lifts a table with all the people of the bar on top of it? He may be strong enough to lift all that weight, right, but the table isn't, and it eventually breaks in half.
- The Resenter: Hercules does not like at all that the Wasp is the team leader.
- Some Nutty Publicity Stunt: Hey, look! Namor has just saved that helicopter from crashing, and saved the two men inside! The protesters against Namor dismissed it, it was surely a setup.
- Spiritual Successor: Most of this arc's Masters of Evil lineup would return years later as the original Thunderbolts.
- Stay in the Kitchen: Namor has left the team, to fight against Attuma, who has invaded Atlantis. The Wasp is a bit angry over this. Hercules says "Facing Attuma alone is a point of honor. But then, I shouldn't expect a woman to understand such things!"