One minute, your teacher was talking about ancient Mesopotamia. The next, gone. There was no poof, boom, or anything else. It was just a sudden disappearance. Everyone was confused. They all looked at each other to see if the other saw what they saw.

(Start however you'd like! Though, your OC can't be over the age of 14! Everyone 15 and up has disappeared, so it would be weird for your OC to be the only one over that age.. Unless you want to, maybe it could stir up some kind of conflict.)