Accidental Magic

This takes place during Harry Potter and the Philosopher's Stone, chapter one, "The Boy Who Lived." (Don't worry, this is not a retelling of the book from Petunia's perspective.) I have always wondered what was contained in the letter Dumbledore left with baby Harry and how the spell of protection Dumbledore spoke of was carried out. So this is my explanation.

We jump ahead to 1997 when Professor Minerva McGonagall remembers a promise she made to Professor Dumbledore shortly after the night Harry Potter lost his parents.

Petunia has something to tell Harry about himself. As well as something about herself.

Harry finally learns about his destiny.

It's Harry's birthday and the time has come for him to receive his gift.

While waiting for his 17th birthday to arrive so he can leave the prison of the Dursleys', Harry learns new information about himself, his aunt, mother and Albus Dumbledore. The information he learns will greatly increase his power while at the same time change how he feels about the woman given the task of raising him.