School lies

In this episode, Serena and her friends made a pool party in their school. Serena called Dan and told him to go with her. But a guy had an accident and they call the ambulance. Chuck finds the school key and hides it.
The next day, the director of the school calls all the students who went to the party and tells them to say the truth. During the next day it will be an individual interrogation to know who was the guilty.
Dan was upset because he has nothing to do with the problem.
In Blair's party, Blair sees that Chuck has the key and take it away from he. She hides it in her room and Nate discovers it, takes it and says that he was the one who opened the school.
But the real thing is that Serena was the one who did it. And she goes with the director and says the truth.
Lily accepted Bart's marriage proposal instead of breaking out with Rufus because Serena tells her not to do that cause she didn't want Dan to be her stepbrother.