Harry and Ginny are married and have three children together. The middle child is having a hard time adapting. He feels like he doesn't really belong and where he fits in, he is the Slytherin House. He has a friend in Draco Malfoy's son, Scorpius. Scorpius also doesn't feel like he belongs. He is rumored to by Voldemort's child. One day before their third year, Albus overhears a conversation between Cedric Diggory's father and his own father, begging for Harry to use an illegal Time-Turner to go back and save his son.
They are prodded on by Delphi who claims to be Cedric's cousin. She keeps getting them to go back, in hopes of changing the past so much that she can make a prophecy come true.
Scorpius points out that because it is predicted, doesn't mean it has to happen. The boys go back in time twice together and Scorpius 2 more times without Albus and once more with Delphi.
This book looks at teens going through life changes, trying to figure out who they are and where they fit. The relationships between the teens and their parents, in this case, the sons and fathers. It also looks at the relationship between Draco and Harry. They come together and learn how each felt about the other and help each other with finding their sons.
I loved the Harry Potter books when they first came out and I have reread them many times. It was fun to see how things continued after Voldemort died and how the main characters grew and changed themselves.