WARNING: The following contains spoilers for What If...? Season 1, Episode 1, "What If... Captain Carter Were the First Avenger," streaming now on Disney+.

Peggy Carter's transformation into Captain Carter differs from Steve Rogers' superhero origin from Captain America: The First Avenger in significant, and even tragic ways. Carter's sheer joy at being part of the action alone helps her stand out from Rogers' more stoic Captain.

Carter's story still takes place as an offshoot of The First Avenger, but while the details do differ, she goes through many of the same challenges as the Captain that Marvel Cinematic Universe fans are familiar with.

RELATED: Marvel's What If...? May Finally Confirm the Fate of a Deadly Hulk Villain

Taking The Super Solider Serum

Super Soldier Peggy What If

The entire alternate reality hinges on Carter being the one who takes the power-granting serum instead of Rogers, and her decision to watch Rogers' procedure from the floor instead of a press box left her in a position to take his place.

An assassin murdered Abraham Erskine and attempted to do the same to Rogers, leaving him in no shape to take the serum. Carter's proximity to the experiment allowed her to take out the assassin and save Rogers' life. It also made her the only candidate to take the serum, helping Howard Stark salvage the only dose left after Erskine's untimely death.

Sidelined By The Allies

Rogers wasn't immediately put into combat. The Allied forces valued his propaganda value over his fighting ability. While scientists tried to reverse-engineer the serum from his blood, Rogers was sent on a USO promotional tour for war bonds instead of joining the fight.

Captain Carter is also benched after taking the serum, due to old fashioned sexism of course. Her superior, Colonel Flynn, thinks the Super Soldier Serum was wasted on her. Beyond dismissing the idea of a female super soldier, Flynn goes to great pains to remind Carter that she should feel "lucky to be in the room" as an agent. Of course, when she becomes a vital part of the war effort, Flynn takes full credit for her success.

RELATED: Hugh Jackman Breaks Fans' Hearts, Completely Rules Out a Wolverine Reprise

Howard Stark, Right Hand Man

As he did for Rogers in The First Avenger, Howard Stark created Captain Carter's Vibranium shield. In this reality, he modifies it with a Union Jack design instead of Captain America's familiar star. He also modifies the costume Carter was going to wear on a USO tour for her first battle with Hydra.

Like he and Carter did for Rogers in The First Avenger, Stark encourages Rogers to go rogue on her first mission. In this case, she's able to capture the Tesseract from Hydra, and Stark uses it to create the Hydra Stomper armor that allows Rogers to join the fight. He even accompanies Carter into the field; something he didn't do for Rogers.

RELATED: Why Marvel's What If...? Won't Introduce Any New Characters to the MCU

Fighting Hydra

What If Captain Carter 2

No matter who's wielding the shield and what reality they're in, Hydra will always be a thorn in any Captain's side. Taking Rogers' place means that Carter becomes the primary opponent of the Nazi Special Forces Unit. Her first battle, where she retrieves the Tesseract and captures Arnim Zola, sees her demolish a Hydra regiment single-handedly.

Like Rogers, Carter spends the rest of her time in World War II battling Hydra and the Nazis. A montage shows her doing considerable damage to enemy forces, taking out ground troops by herself. She also cuts a swathe through the German air force with an assist from Rogers and his Hydra Stomper armor. But Rogers isn't the only ally she picks up during the war.

Fighting Alongside the Howling Commandos

After Bucky Barnes and his unit are captured by enemy forces, Carter goes on a solo rescue mission as a personal favor to Rogers. Like Rogers in his first mission, Carter frees Barnes and the legendary Howling Commandos. She does get an assist from Rogers, debuting his Hydra Stomper armor to neutralize some enemy tanks trying to impede their escape.

RELATED: Ms. Marvel: Why Kamala Khan Took Up Carol Danvers' Old Mantle

The Commandos accompany Carter in subsequent adventures, backing her up during Operation: Where Eagles Dare, when she's able to save Bucky from falling from the train that the team boards. That prevents him from suffering the fate of becoming the Winter Soldier. The Commandos also accompany Carter on her mission to foil the Red Skull's ultimate plan for the Tesseract.

Tragedy On A Train

What If Captain Carter Howling Commandos

Before they were parted for good, Carter thought she'd lost Rogers on a mission. Rogers provided backup for Carter and the Howling Commandos during Operation: Where Eagles Dare. The operation was an attempt to take out Red Skull and end the war for good. Bucky thought the idea smelled "as fresh as three-day-old fish."

His skepticism turned out to be well founded, because the train was packed with dynamite. Rogers was able to warn his allies in time for them to get off the train, but he wasn't as lucky. The explosion and the avalanche it caused left no trace of the Hydra Stomper or its pilot. Carter's grief led her to interrogate Zola, who told her about Red Skull's plans for world domination. It's a variation of Bucky's apparent demise in The First Avenger.

RELATED: Loki's He Who Remains Understands He's the Villain of the Story

 The Carter/Rogers Romance

The romance between Carter and Rogers transcends at least one alternate reality, in spite of the wildly different dynamic between them in What If...? Even though he's still a sickly kid from Brooklyn, Rogers forms a bond with the empowered Carter.

Piloting the Hydra Stomper puts them on more equitable footing, but it's clear that Carter was taking a shine to him even before he could join her in battle. Just like in the MCU, their flirtation leads to plans for a dance that go unfulfilled. Like Rogers, Carter has to break their date to save the world, leaving their love unrequited.

Heroic Sacrifice

Peggy vs tentacle monster what If

Like Rogers, Carter sacrificed herself to stop the Red Skull's plans with the Tesseract from coming to fruition. In both cases, the Skull was hoist on his own petard in the process. And while Red Skull suffered a fate worse than death in the MCU, he meets a more gruesome end in What If...?, crushed by the tentacles of an eldritch horror he summoned.

RELATED: What If...?'s Marvel Zombies Draws More From the Comics Than Any Other Episode

All of Carter's allies try to lend a hand in stopping the beast from making it out of the portal. This includes Rogers' assistance, whom the Howling Commandos find imprisoned in the Red Skull's castle. While Stark figures out how to shut down the portal, in spite of not understanding German, no one can help Carter physically push the beast back.

Rogers expends energy he might have used to push the monster through the portal to get the Commandos to safety. His last attempt to back up Carter leads to his suit shutting down. He can only watch as the love of his life goes through the portal, which seals behind her, causing an explosion of energy.

A Woman Out Of Time

In the episode's final scene, Carter emerges from a Tesseract-created portal. She looked to be the same age as she was when we last saw her. Still carrying the same sword she picked up in the Skull's castle, she had put it to good use on the other side of the portal, going by all of the pieces of tentacle that preceded her entrance.

RELATED: What If...? Creators Tried to Make a Marvel/Star Wars Crossover Happen

She's met by two familiar faces from the MCU: Nick Fury and Hawkeye. When Carter asks Fury where Rogers is, he informs her that it's been nearly 70 years since the end of the war. A despondent Carter tries to take solace in the fact that the allies won.

The ending parallels the last scene of The First Avenger, with Rogers waking up in modern day America after his long slumber and being greeted by Fury. Given that this isn't the last we'll see of Captain Carter's story in What If...?, it wouldn't be surprising if she continues to follow in the MCU Rogers' footsteps and joins the Avengers in a later episode.

The first excited episode of What If...?, focusing on Captain Carter, is now available on Disney+, with new episodes becoming available on Wednesdays.

KEEP READING: Spider-Man's Most Disgusting Power Is Too Horrific to Appear in the MCU (We Hope)