It's been a while since we've been to Hogwarts…and we're amped.
We're going to run through the wall at Platform 9 ¾, hitch a ride on the Hogwarts Express, and get sorted into a House (we're totally Ravenclaw). It'll be like The Wizarding World Of Harry Potter come to life: everyone gets sugar buzzed on Butter Beer and has an amazing, magical time.
Unless, of course, you're Albus Severus Potter, son of Harry Potter.
Albus is over the whole Hogwarts thing before he even gets there. Not only is he sorted into Slytherin—let's hope he inherited his dad's fluency in Parseltongue—he has trouble flying, stinks at Quidditch, and is known as Harry Potter's "disappointing son." (1.4.61) That's got to sting more than an expelliarmus spell between the eyes.
However, there's a fizzing whizbee buried in this pile of centaur dung that is Albus' life. He finds his best friend, Scorpius Malfoy. By their fourth year, the pair is inseparable, despite Harry's wish that his son not be friends with his childhood rival's kid.
Oh, and there's the little matter of a rumor that Scorpius is actually Voldemort's son. The-rumored-son-of-he-who-must-not-be-named is the longest nickname ever, so we'll ignore that rumor for a while. Albus doesn't believe it anyway. (There's no way Voldemort could have had a kid with a nose.)
Before his fourth year, Albus gets into a huge argument with his dad. Harry tireless tries to convince Albus that Hogwarts is paradise on Earth, while Albus essentially says, "Dad I go there; you don't understand."
Unable to bridge the gap between them, Albus says he wishes Harry wasn't his dad, and Harry says he wishes Albus wasn't his son. (Silver lining: Albus can now save all the allowance money he would have spent on "#1 Dad" mugs over the years.)
After overhearing a conversation between his dad and Amos Diggory, dad of Cedric "Deader than Dead by Now" Diggory, Albus gets an idea: he'll fix his father's past mistakes by using a Time-Turner to go back to the Triwizard Tournament and keep Cedric from dying.
What could go wrong?
With the help of Scorpius and Amos' niece, Delphi Diggory, Albus retrieves a hidden Time-Turner from the Minister for Magic's office. Did we mention the Minister is Hermione Granger-Weasley? No? Well, the Minister is Hermione Granger-Weasley. And she displays uncharacteristic stupidity by hiding a dangerous magical device in her bookcase.
Thanks to Hermione's lax security, Albus and Scorpius whiz into the past. Disguised in Durmstrang robes given to them by Delphi, they expelliarmus Cedric's wand out of his hand during the dragon task. They return to the present to find things changed unexpectedly. Cedric still died. (RIP, bro.) And Hermione and Ron never married, meaning they never had Rose, the girl Scorpius has a crush on.
Harry, on advice from a psychic centaur in the woods, tells Albus to stop hanging out with his only friend, Scorpius, because he believes him to be a bad influence on him. As you might guess, this does nothing to strengthen his relationship with his father. Meanwhile, Ron is boring and Hermione is a bitter old lady who teaches Defense Against the Dark Arts. The world just ain't right.
That means it's back to the past again. This time, Albus and Scorpius inflate Cedric like a balloon during the underwater task. Returning to the present, Albus disappears, leaving Scorpius alone in the lake. He is fished out by Dolores Umbridge, who's replaced Professor McGonagall as Headmistress of Hogwarts.
Umbridge tells Scorpius that it's Voldemort Day, and over the next few days, Scorpius learns that a) Harry Potter is dead, b) Cedric Diggory became a Death Eater who killed Neville Longbottom, and c) Scorpius is really popular. He's like the new Harry Potter. His dad, Draco, is the Head of Magical Law Enforcement, which is the job Harry held in the "real" timeline. He abuses his power by torturing Muggles. We're not sure how that enforces magical law…and neither is Scorpius.
Realizing that he is "better off in this world. But the world is not better," (3.9.56) Scorpius decides to head into the past again to make sure Harry Potter doesn't turn into the Boy Who Lived But Then Later Died. He recruits Snape to help him, and Snape leads him to Hermione, a frazzled freedom fighter hiding in the woods. They travel to right before Albus tries to zap Cedric, and Hermione blocks his spell.
Back in the "Harry's dead" timeline, they return just in time to feel the effects of space and time be pulled apart. Ron and Hermione are consumed by Dementors, and Snape defends Scorpius until the timeline fixes itself, returning Scorpius back to the original timeline. Albus is back, and their parents are furious with them, but Scorpius tries to convince Albus how good he has it. Harry Potter may be his dad, but at least he's alive.
For some reason (i.e., he's fifteen) Scorpius lies about losing the Time-Turner. He still has the device in his possession, and he wants to destroy it with Albus in a spectacular fashion. Albus invites Delphi…because this was 1/3 her idea in the beginning. When she finds out that they created an alternate timeline where Voldemort took charge, she reveals that she is actually (le gasp!) Voldemort's daughter.
All she wants is to meet her dad, so she wants to go back in time (again) to meet him. While she's monologuing her villainous diatribe, an innocent student shows up and Delphi avada kedavra's him to death. So sad.
Zap. Back we go to the final challenge in the Triwizard Tournament. Delphi threatens Scorpius with death to get Albus to humiliate Cedric's fragile wittle feelings and turn him into a Death Eater, but Albus and Scorpius manage to escape her clutches and allow Cedric to go to his death, which is how things are supposed to go.
Angry, Delphi uses the Time-Turner to send them backward, then smashes it and runs away. Albus and Scorpius speculate that Delphi will try a different tactic to meet her father—go to Godric's Hollow right before Voldemort kills Harry and just say, "Hi, dad." They follow her to Godric's Hollow and, using Harry's baby blanket, send a magical message to present-day Harry.
Present-day Harry, who hasn't been at Hogwarts for over twenty years and still hasn't said a nice word to Draco Malfoy, is forced to work with him when Draco reveals that he has a conveniently hidden second Time-Turner. The whole gang—Harry, Draco, Ron, Hermione, and Ginny—go back to the day Harry's parents are killed, and they find Scorpius and Albus.
But how to stop Delphi? Harry decides to trick her by transfiguring himself into Voldemort. Disguised as Voldemort, Harry approaches his parents' house as if he's going to kill his own parents. Delphi shows up, but she quickly sees through Harry's disguise. A magical duel ensues, and it ends with Delphi bound on the floor. She begs to be allowed to see her own father, and Harry denies her request. Stone cold.
Before returning to the present, Harry realizes he must watch his parents die at Voldemort's hands. The real Voldemort enters, and Harry collapses in torment after watching him slaughter Harry's parents. Everyone returns to their normal timeline.
Flash forward a few days. Scorpius has found inner confidence after saving the day in another timeline. And taking a walk in a graveyard—like you do—Harry promises he'll try and be a better dad to Albus.