You were sent back in time by present day Dumbledore with the help of a time turner to stop Voldemort when he was still Tom Riddle and Dumbledore had you privately sorted into Gryffindor to avoid suspicion that you’d done something if you saw Tom.

Tom, being completely unaware that you’d just caused his future plans become the most powerful and feared wizard in the entirety of the Wizarding World had been foiled by your simple and secret trip into the past.

He was sat at the back of the class with a book of Dark Magic infront of him as he was studying each page like it was a manuscript, he wasn’t even paying attention to the conversations or anything happening around him, but keeping alert.

When you walk in his eyes flicker up to yours and you don’t say anything but just go sit down in your chair in the corner of the room and go through your own book on Charms that you had.

You kept to yourself while he had no idea what you’d done and he could no longer become the powerful wizard he wanted to be and he would stay who he is and nothing bad would be able to happen and his Death Eaters would never be assembled due to Voldemort never existing.