On Teen Wolf Season 6 Episode 1, Stiles is getting annoyed that it's been 3 months since a supernatural attack, while Scott is happy that Beacon Hills is learning how to exist without their help. They will be leaving for college soon, so they can't protect Beacon Hills forever.
Liam and Hayden come across a kid, Alex, alone in a car. His parents have been taken in a car accident, and when Scott sees inside Alex's head (you know, through the alpha claw trick), Scott discovers that a guy on horseback took Alex's parents.
Scott and Stiles go to Alex's house, and they learn that it is deserted, except for Alex's room. While Liam and Mason update Scott on the weird compasses downstairs, Stiles sees the Ghost Riders, and he is shot at. The ghost rider misses, but the damage has been done.
Lydia figures out that the Wild Hunt has come to Beacon Hills. By the time Stiles realizes he is the next target, it's too late. Everyone has forgotten him, everyone but Lydia. Stiles begs her to find a way to remember him, but as we jump forward to, assumedly, the next day at school, Lydia has forgotten Stiles.