This is the (admittedly short) prologue to Harry Potter and the Black Doorway.  Similarly to the way the original books were written, it is from a completely different perspective than anything else, and probably won't make sense until about three-quarters of the way through the story.

Specifically, roughly two years after Voldemort's defeat, a few Durmstrang graduates appear to be checking on a new birth.

This brief chapter details the trip from Platform 9 3/4 to Hogwarts, and introduces the Potters.  This chapter takes place on the same day as the Epilogue. I swear, the chapters start getting longer after this.

This chapter covers the fallout of Albus's sorting, giving both himself and Sypha a poo rintroduction to inter-house relations.

As the first week of term comes to a close and the Potter brothers are forced to interact again, Sypha is met by a being in the shape of an owl, the presence of which will taint both her and the lives of her friends at the school.

In the immediate aftermath of Sypha's collapse on Halloween, the teachers attempt to determine why she reacted so violently to the Patronus spell, her friends visit and make plans for Hogsmeade, and a second member of the oritinal trio makes an appearance.

Eight days before the end of term, something terrible happens.