Ted and Barney pose as tourists to pick up on a couple of New York women, and Robin starts getting fed up with her new boyfriend.
Marissa throws a birthday party for Trey - an event that may or may not smooth things between the two Atwood brothers.
Nana's getting married - news that has Sandy, Seth and Ryan off to Miami. Back in the OC, Zach wows Summer with a home-cooked meal, Kirsten sorts out her Carter feelings and Trey's feelings for Marissa take a terrifying turn.
The evidence adds up. Trey is likely to do time for drug violations, but Sandy, Ryan and Marissa know he's innocent and develop a plan to catch the real culprit in the act.
Familiar faces show up for a final farewell to Caleb. Meanwhile, Sandy takes action to help Kirsten.