You were heading back to your dorm for the evening when you heard strange noises coming from the girls bathroom, so you decided to go check them out.

Moving slowly towards it you look in and see someone by the sinks, this just happens to be Tom Riddle, speaking in a weird language by one of the sinks.

Suddenly a secret passage opens and he heads down it, this was leading to only one place, The Chamber of Secrets.

You followed him as he went down there, making sure not to be seen or heard.