The O.C. season 1 episode 26
Episode title: The Strip
It's Bachelor and Bachelorette party time for Caleb and Julie. Caleb and the boys head off to Las Vegas while Kirsten organizes an evening at the Cohen house for Julie, strippers included. Seth and Ryan get themselves into a tricky situation in Vegas while back home, Summer pines over lost love, and Marissa comforts Theresa. Jimmy and Sandy learn of Caleb's true motives. Julie and Hailey take a swim, while Theresa has some shocking news for Ryan and Marissa.
