Scorpius enters Headmistress Dolores Umbridge's office with a different set of clothes. Umbridge tells Scorpius that she has always seen him as a Head Boy. He is a natural leader and a great Quidditch player, which comes as a surprise. He's never liked Quidditch. And yet, ever since she found him in the lake three days prior, she's noticed that he has an obsession with Harry Potter, and is constantly asking people about Cedric Diggory and the Battle of Hogwarts. The Headmistress asks if there is something she can do to get the old Scorpius back. He insists that he'll soon return to normal. Umbridge smiles. She then places a hand to her heart and says, "For Voldemort and Valor."

Walking the Hogwarts grounds, Scorpius bumps into Karl Jenkins and Yann Fredericks. They remind him of their plans to torture Mudbloods in the dungeons tomorrow night. Scorpius is surprised to learn that this was his idea. Then Polly Chapman invites Scorpius (addressing him as "The Scorpion King") to something called the Blood Ball. Then Polly notices blood on her shoes and uses the term "Potter" as a curse word. In response to his confusion over the Blood Ball, she tells Scorpius that the Augury says the future is theirs to make, and she's making hers with him. Then Polly exits saying, "For Voldemort and Valor". Scorpius repeats the phrase.

Now at the Ministry, Scorpius enters the office of the Head of Magical Law Enforcement and finds his father, Draco Malfoy, sitting at what was formerly Harry Potter's desk. Draco is angry. His son kept him waiting and did not apologize. He demands that Scorpius not humiliate him at Hogwarts by asking questions about Harry Potter. Scorpius asks if Draco was involved in the Muggle-born death camps, and asks what his mother felt about it. Draco tells him not to use his mother's name in vain, then reveals that he had no part in the Death camps. His wife was sympathetic to Muggle-borns, which is why Lucius Malfoy disliked her. But Draco defied his own father for Astoria. Apparently, it was the bravest thing she'd ever seen. Scorpius confesses that he doesn't want to be the person he is now. That he wants to be more like his mother. Draco says that she always helped him find the light in the darkness. Draco tells his son that whatever he plans to do, he needs to do it safely. Draco doesn't want to lose his son as well.

Scorpius is in the Hogwarts library trying to learn how Cedric became a Death Eater, when Craig Bowker Jr. asks why he's there. Scorpius asks why he can't be. Craig quickly grovels and apologizes, stating that the Potions homework wasn't ready. Scorpius then realizes that, in this new reality, Craig does his homework for him. Craig tells Scorpius that Professor Snape's assignments are very difficult, but he is honored to complete the Scorpion King's work. The realization sets in that Severus Snape must still be alive...

Scorpius enters the Potions classroom, where he asks Snape if he is still working for Dumbledore. Snape denies ever doing so, beyond his teaching duties while Dumbledore was Headmaster. Scorpius confesses that he knows Snape secretly spied on the Death Eaters for Dumbledore and then killed him as a part of their plan. Scorpius continues by telling Snape about the Time-Turner and how he's from an alternate universe where Harry Potter succeeded in defeating Voldemort. Snape states that Harry Potter won the Triwizard Tournament. Scorpius counters with his own history, that Cedric was meant to win as well, but they humiliated him and he became a Death Eater. Snape tells him that Cedric killed Neville Longbottom, causing Scorpius to realize that this is what truly changed the future. Neville was supposed to kill Nagini, the final Horcrux, before Voldemort died.

This narrative is too much for Snape to believe, so Scorpius reveals a secret only known to Albus Dumbledore: that Professor Snape loved Lily Potter! Scorpius tells Snape that Harry is alive, and that he named his son Albus Severus. Deeply moved by this, Snape takes out his wand and locks the door. He tells Scorpius that they need to go to a hidden room in the roots of the Whomping Willow.

Once there, Scorpius is pinned to the table by Hermione. She is apparently a rebel, leading the resistance against Voldemort. Snape tells him that Scorpius is trustworthy, so Hermione lets him go. Scorpius confesses that this version of the world is his fault. Before he can clarify, Ron enters, notices Scorpius, and points a wand at him, rather awkwardly. Hermione and Snape explain that Scorpius is on their side.

"Rebel Hermione" inspects the Time-Turner, while Ron tries to understand why their future rests on Neville Longbottom. Ron tells Scorpius that he and Hermione are fugitives, and that there are barely any members left in Dumbledore's Army. Scorpius reveals that, in the other reality, Harry is the Head of Magical Law Enforcement and that Hermione is the Minister of Magic. Hermione is happy to hear this, and Ron asks what he does for a living. Scorpius says that he runs the joke shop, but is mostly a stay-at-home dad. Oh, and that he is married to Hermione. Hermione inquires about Snape's fate. Before Scorpius can answer, Snape interjects that he is presumably dead, since Scorpius acted so surprised when they met.

The four of them venture to the edge of the Forbidden Forest to aid Scorpius in returning to the past so they can reset everything back to the way it was. Once there, they plan to block the spell that Albus used to prevent Cedric from succeeding in the first task. Snape warns Hermione that the dementors will be looking for her, but she doesn't care.

We now see the same sequence as in the first task of the Triwizard Tournament. Hermione notices Albus beginning to cast his spell on Cedric's wand and blocks the spell, allowing Cedric to win the task.

Hermione, Scorpius, Ron, and Snape return to the Forbidden Forest in the alternate present. Ron is in pain, and Scorpius tells him that Albus had gotten hurt during their trip. Snape warns them, all too late, that they are out in the open and, therefore, vulnerable to attack. But the dementors are already descending on the group. Hermione knows that they're only looking for her. She declares her love to Ron and tells them all to flee, that she'll stay behind and let the dementors take her. Snape and Scorpius run, but Ron stays behind. He likes the idea of both of them being married and having children. Hermione tells him to kiss her. The pair kiss as the Dementors suck out their souls.

Snape and Scorpius continue to run, but a Dementor appears in front of Scorpius. Snape tells him to think of the thing he loves. He thinks of Albus, and then begins to hear his mother dying, and knows he can't defeat the Dementor. Snape reminds him he is doing this to save Harry Potter and his friend. Suddenly, Dolores Umbridge arrives and tells him that Hermione was caught by the Dementors. They both act happy, but Umbridge knows that she was with Snape and Scorpius. Snape tries to leave, telling Umbridge that they are late for class. She stops them, pointing out that they are on their way to the lake instead of the school. Snape realizes that she knows about his secret loyalty to the resistance. Umbridge confirms that she has suspected for years that Snape was against Voldemort's rule.

Professor Snape disarms her and casts a Patronus. Scorpius sees that it's a doe, like Lily Potter's Patronus. Snape orders Scorpius to run, but first asks him to tell Albus that he's proud the boy carries his name. Scorpius enters the lake and activates the Time-Turner. He ascends to the surface, and so does Albus. Scorpius is overjoyed to see his friend alive, but Albus is confused. He saw him only two minutes ago. Scorpius hugs Albus and checks his school uniform. He's wearing Slytherin robes. Harry and company arrive and ask what happened. Scorpius claims to have lost the Time-Turner in the lake.

After the entire story is explained to Professor McGonagall, she considers expelling the boys, but wryly states that it would be safer if they remained under her care. So, she gives them detention for the rest of the year, cancels Christmas, and bans them from Hogsmeade. Suddenly, Hermione enters through the door and McGonagall jokes about giving Hermione detention for keeping an illegal Time-Turner in a bookcase. The Headmistress tells the boys that their goal to save Cedric was honorable, but not if it ends up plunging the entire wizarding world into darkness. Lastly, she orders everyone to leave her office and to find the Time-Turner.

Albus is sitting in his room in the Slytherin dormitory when Harry enters. His father tells him that they haven't found the Time-Turner, and asks why he traveled back in time in the first place. Albus confesses that he wanted to change what happened to Cedric. That it was unfair. Harry agrees, but says that Albus didn't have to risk his life. What he did was stupid and reckless. However, Harry apologizes for thinking that Scorpius was Bane's black cloud and the son of Voldemort. Harry reveals to Albus how scared both he and Ginny were, and Albus replies that he thought "Harry Potter" wasn't afraid of anything.

Albus further tells his father that after saving Cedric from the first task, he'd been sorted into Gryffindor. But that the two of them were still fighting, even then. Meaning that being sorted into Slytherin was not the root of their issues. Harry agreed, but this doesn't solve their problem.