Everything starts when Friday Thirteen (the girl, not the date) gets thirteen years old.
Friday should be worrying only about how to stop the stupid nicknames like "Frost Witch". But her grandmother has another plans, which includes Friday traveling more than seventy years (so, seventy-four) for the past.
Let it be clear: Friday Addams is a fantasy book addicted, she have read and watched Harry Potter more than seven times, and have read Percy Jackson more than twelve.
She has even more experience with Time Travel fanfictions and Interdimensional Travel stories. So, quickly, she realizes she's in the fucking Hogwarts Express and Harry fucking Potter is faking to be an muggle-born called Harry Evans. And why's that?
Friday's dreams are coming true. Somehow she traveled to a typical Harrymort/Tomarry fanfiction.