While in the midst of searching for the Hulk following his departure in the previous episode, Iron Man starts picking up a faint life sign but can't pinpoint its exact location. That's where Wasp comes in, although not quite in the manner that anyone had in mind. She does not find the Hulk but a shield with a red, white, and blue pattern, frozen in the ice. As it turns out, Captain America was not thrown into a watery grave but was somehow able to survive, albeit just barely.
The Cap is defrosted on board the quinjet and regains consciousness completely disoriented. Thinking that the Avengers are in fact HYDRA agents, he takes them all down and bails out over New York City; the decades he spent frozen in ice do not appear to have noticeably diminished his fighting skills or athletic ability. Meanwhile Black Panther acts on his own, inscrutable motives, breaking into Avengers Mansion and downloading details on all the heroes.
Attempts to reason with Captain America end in failure, largely due to Thor's insistence on smiting first and asking questions later. The fight is only stopped when the Cap turns and notices that a large crowd of tourists has gathered to snap photos of the confrontation. Confused, he begins to realize that this is a world quite unlike the one he left behind after the Red Skull's escape — a world where he and Bucky died.
The Cap's return also catches the attention of HYDRA, which is in the midst of a small leadership crisis now that its former leader, Baron Zemo, has escaped from the Raft. Upon hearing the news, Zemo decides to give up his claim, taking only the scientist Arnim Zola and declaring that he is only interested in revenge. The audience is then treated to a small flashback to World War II where Zemo was in charge of a bio lab tasked with creating monsters and an even more sinister weapon: Virus X. Captain America and Bucky destroyed the lab and Zemo was immersed in his own concoction, requiring regular treatments from Zola to stay alive. In the decades since the war, Zola's technology and capabilities have improved but he has not been able to find a cure for Virus X. He speculates that Captain America's DNA, enhanced by the Super Soldier Serum, might hold the key to a cure and the two friends begin plotting.
The Avengers take the Cap back to the Mansion, filling him in on what has happened to the world in his absence. He was an inspiration to the entire nation and left behind a great legacy, but this is a cold comfort to the Cap now that everyone he ever knew and loved is gone. He leaves to be alone with his thoughts while the Avengers respond to an emergency call back at Ellis Island, which is being menaced by Zola's giant blob monsters. One of them also attacks the Mansion, leaving Cap and Wasp to fend for themselves. Wasp's bio-stingers actually manage to take down the blob monster unlike the efforts of the other Avengers. She is unable to actually savor her victory thanks to the arrival of Baron Zemo.
Zemo's attacks take their toll on Captain America and he is hard-pressed to fight without his shield. Just as Zemo is about to deliver the coup de grâce, however, the Black Panther shows up and tosses him the mighty shield, allowing the Cap to regain the upper hand. Zemo remains defiant, claiming that the future belongs to him but Cap rejects this sentiment:
The Avengers continue to struggle against the blob monsters, which have merged into one gigantic blob monster that keeps growing thanks to Thor's lightning. In his last moments, Thor is disturbed that mortal science could have created such a monstrosity but just when all seems lost, Cap and Wasp show up to help free the others. Wasp is once again the most effective combatant against the blob monster and Cap identifies the creature as one of Zola's creations. Ant-Man is hit by a sudden inspiration and reconfigures his helmet to start emitting energy waves that drive the creature back. As it turns out, Zola's monsters all share a common weakness: they're really unstable and the right type of energy (like Wasp's bio-stingers) can exacerbate that instability. After Iron Man reconfigures his repulsors to give off the same type of energy, the monster is defeated. The cheering crowds that emerge convince the Cap that maybe, just maybe, he's not as obsolete in the modern world as he thought.
Later, Tony gives Cap an old keepsake of his: a photo of his father Howard Stark with Cap and Bucky. He also invites Cap to join the Avengers, which he happily accepts. Cap then asks to meet the Avenger who saved him during the fight at the Mansion, leaving Stark totally confused. Zemo returns to Zola's secret hideout to begin plotting his next move, but the Enchantress makes him an offer he can't refuse.
Tropes:
- Achilles' Heel: Hank knows from experience that Zola's creations suffer from the same instability and that specific types of energy signatures can exacerbate it.
- Apologetic Attacker: Wasp after zapping Cap. She just wanted to get his attention so that she could show him the memorial statues.
- Bait-and-Switch: As Zemo enters Zola's lab, Doughboy appears to be menacing him, but Zola says he's just excited. Doughboy happily puts a tendril on Zemo's shoulder.
- Be Careful What You Wish For: After getting his shield back, Cap reminds Zemo that he wanted this fight and wipes the floor with him.
- Big Damn Heroes: Black Panther throwing the shield in-between Zemo's sword and Cap.
- Covered in Gunge: Defeating Doughboy leaves the Avengers and the surrounding area covered in gunk.Thor: Victory... is ours.
Wasp: Hooray. - Curb-Stomp Battle: Zemo versus Reaper lasts all of two seconds before Zemo severs Reaper's arm and knocks him on his ass.
- Deal with the Devil: Zemo is made an offer by the Enchantress.
- Death Glare: When a mook enters to deliver news of Cap's return to Strucker, Zemo openly glares at him. The guy clearly notices this and clarifies his word choice.
- Dramatic Irony: While fighting Zola's Doughboys, Iron Man quips that he's glad Cap is sitting this one out because they probably didn't have this in the 40's, when we already saw a Doughboy during the flashback to one of Cap and Zemo's fights.
- Dynamic Entry: Zemo enters HYDRA Island's control room by blasting the door open.
- Establishing Character Moment: Zemo effortlessly taking down the show's Adaptational Badass, the Grim Reaper.
- Evil Cannot Comprehend Good: Averted. Zemo knows Cap will always care more about protecting others than capturing him, so he makes his escape by throwing a bomb at the unconscious Wasp.
- Evil Counterpart: During the flashback, Zemo hypes himself up as this to Cap by saying he's found a way to outdo the Super Soldier formula. Cap nonetheless outdoes him because he doesn't rely on speed and strength.
- Flashback: To Italy 1943, where Cap and Bucky attacked Zemo's operation. This is how Zemo was exposed to Virus X.
- Flashback Nightmare: Cap is having a nightmare about Bucky's last moments before waking up.
- Funny Background Event: A patriotic pin-up poster can be seen on the wall of the room Tony prepared for Cap.
- Heroic BSoD:Captain America: I should never have woken up. I'm a soldier, not some future-man. I can't imagine a world that's changed so much still needs Captain America.
- Hoist by His Own Petard: During the flashback, Zemo tried to spray Cap with Virus X. Cap responds by using his shield to break open the vat behind Zemo, exposing him to it instead.
- Irony: Cap reflects on how everyone from his old life is gone, only to later see for himself that one of his least favorite people also made it to the 21st century.
- It's a Long Story: When Captain America asks if she's one of Zemo's experiments, Wasp is about to explain her origin, but then she just says it's complicated.
- Mythology Gag:
- Zemo's costume during the World War II days.
- Thor remarks that Cap "will not yield" — a reference to Cap's infamously cheesy theme song from the 1960s Marvel Super Heroes cartoons.
- Negated Moment of Awesome: Zemo and Strucker are about to throw down for control of HYDRA, but then a mook alerts them to Cap's return.
- Noodle Incident: Hank previously studied some of Zola's creatures.
- Oh, Crap!: Cap when he sees the memorial statue to him and Bucky.
- One-Man Army: Captain America vs. the Avengers. Granted, they're not trying to hurt him, but they sure aren't able to corral him, either. It takes Wasp showing him the memorial statues for him to stand down.
- The Only One Allowed to Defeat You: Zemo is quite relieved to learn that the Red Skull failed to kill Cap after all."Let the Skull have Bucky. Your life is mine to take!"
- "The Reason You Suck" Speech: Zemo to Cap."I have evolved my body over the years, while you remain as you ever were. You are alone, Captain; a relic in this world."
- Revenge Before Reason: Zemo would rather kill Captain America on his own than use all the resources of HYDRA.
- Shut Up, Hannibal!:Zemo: This is my world, and you don't belong in it!
Captain America: I may not know a lot about the future, but I know one thing about the past: you lost the war. You'll always lose, whether I'm here or not. - The Slow Path: Zemo notes that he's "evolved" in order to live on in the years after World War II. He feels he has adapted to the present day, as a result, and dismisses Cap as a relic that simply woke up into it.
- Stranger in a Familiar Land: Captain America"Bucky's gone. Everyone I ever knew... my whole world... it's all gone, isn't it?" (puts down his shield and walks away)
- The Starscream: It's revealed that Strucker runs HYDRA now because he betrayed Zemo and left him to rot in prison.
- Super-Soldier: Captain America, of course, but Zola also notes that acquiring a sample of Cap's DNA was intended to both cure Zemo's condition and mass-produce an army of these.
- Undying Loyalty: The HYDRA mooks don't hesitate to bow before Zemo.
- Villain Respect:
- Zola is openly amazed that Captain America is still alive, crediting it to the Super Soldier formula.
- Zemo admits that Cap's skills are every bit as "perfect" as he remembers them being.
- We Meet Again: How Zemo greets Cap at the mansion.
- Wham Shot: Zemo encountering Amora and Skurge in Zola's lab.
- Wouldn't Hit a Girl: During Cap's fight with the Avengers, Wasp is the only one he doesn't try to take a swing at, even though he genuinely thinks she's a HYDRA agent and knows she zapped him.
