Gossip Girl Season 1 Episode 12

Serena, Blair, Nate, Chuck and their entourage break into the school swimming pool for a night of fun, but when a member of their group nearly drowns, the school threatens to expel the person responsible for the break-in. Everyone agrees to keep a secret pact and say nothing, but it ultimately creates major tension between Serena and Dan, who isn't sure he's ready to take the fall for someone else and risk his future.