Marissa plots to ruin her mother's happiness by inviting someone from her mother's past to the wedding shower, while Sandy attempts to hide Theresa's return to the O.C. from Ryan. When Ryan discovers Sandy's lies and Theresa's reasons for coming back, he puts himself in a dangerous situation. In the meantime, Seth's unimpressive first meeting with Summer's father leaves their relationship in doubt.

Julie and Caleb walk down the aisle, as Ryan and Theresa face a difficult decision regarding their pregnancy. Marissa moves into Caleb and Julie's new castle on the cliff, and Seth struggles to find himself when things around him seem to fall apart. Life in The O.C. comes full circle from one year before.