By Daniel Barron for AllPop

It's the last episode of the season and we all know something crazy is going to happen, but what? Something that will change the face of the O.C. forever occurs in the last few minutes of The Graduates.

We start the episode off at the Cohen's as Ryan and Kirsten wait anxiously for Sandy and Seth to get home from the police station where Seth is being questioned about what happened at the Newport Group offices. They finally do get home late and Sandy tells Kirsten that Seth denied everything. Meanwhile in the poolhouse, Seth tells Ryan he doesn't know how to tell his dad that he really did burn the office down. Sandy is suspicious that something is up but can't accuse Seth of anything, even though he was the last one seen on the security cameras.

Seth decides he wants to listen to some depressing music and goes to get his iPod in his mom's car. Ryan says he'll get it as he left the car on the street anyways and wants to move it. As he walks to the car, Volchok shows up, obviously in a panic. He needs help but Ryan wants none of it. As he leaves, he tells Ryan that if he's going down, Ryan's going down with him.

The next day, Summer, Marissa and Taylor are helping put together the graduation decorations at the Harbor School when Julie shows up. She has a gift that was sent to her by her dad. Marissa goes off on her own to see exactly what it is.

Back at the Cohen's, Kirsten answers the doorbell and sees Dawn at the front door. They hug and Ryan comes down to greet her as well.

Kaitlyn also shows up at the Roberts' house later that day. She says she wouldn't want to miss a graduation. Neil says that was very nice of her to support her older sister and Julie thinks it's almost too nice; seems she's suspicious that Kaitlyn is there for more than just support.

The hours are counting down to the graduation ceremony and Seth has a one-on-one talk with his dad. First he asks Sandy not to embarrass him at the graduation … then comes clean about starting the fire at the office. Sandy is disappointed but glad Seth came clean. Seth says he's been lying so much recently because Sandy was so busy with work and he didn't want to upset Kirsten. Sandy admits he made some mistakes as well. He tells his son that they should just forget about all the problems if only for the night, because nothing should ruin graduation.

At Harbor, Marissa sits Summer down and tells her that Jimmy offered Marissa a job doing manual labour (??) for a year while he sails different boats for rich people. It's not the kind of job one would expect Marissa to do but she states simply that it's the chance for a new life; she needs a change, and this is the perfect opportunity. Summer is sad, as expected, but supports her best friend's decision.

We then catch up with Volchok, who is hiding out in Heather's van. He's completely paranoid about being busted by the police. He says he just needs some money to leave town, but Heather thinks he's waiting for more than just cash - he's also waiting for Marissa. He screwed things up with her, but now he wants her back.

It's almost time for the graduation ceremony, and everyone, including the gang, is in their cap and gown. Marissa pulls Ryan aside and tells him about what she's going to do for the next year. He's just as understanding as Summer was, and only asks that he can drive Marissa to the airport when she leaves the next day. She was the first one he met in Newport, so he'd like to be the last one she says goodbye to.

So the ceremony commences, with Taylor acting as valedictorian. There's much smiling, cheering, and especially crying from all the of the moms. Afterward there's a family-only party. Sandy does a quick speech and toast to the kids. Over the last three years, he says, there's been tragedy, comedy, first loves, broken hearts, family members lost and found. Summer finds this especially touching and starts crying. She tells Seth she's worried about everyone being split up next year, including them specifically. Seth says that whatever happens, they'll make it work. Marissa breaks the news of her travelling to her mom, but Julie tells her that she already knew about it; Jimmy called her before sending the gift to Marissa to make sure Julie was okay with it. Kaitlyn pops up to tell Julie that she's moving back to Newport for good, as she's sure her mom will still need a daughter there.

Ryan gets a great little present of his own from his mom - a truck. Her boyfriend helped her get it and fix it up and now it's all Ryan's.

Marissa hears her cell phone ring and answers it. It's Volchok on the other line. He wants to see her but she refuses. He tells her that if she doesn't see him, he'll make life hell for Ryan. All he has to do is tell the police about the car they stole together. Marissa doesn't believe that Ryan stole a car but Volchok tells her to ask Ryan herself. She does, and Ryan explains what exactly happened. They both decide it's time to get Volchok out of their lives forever and Marissa wants to help.

The next morning, Dawn says goodbye to her son and the Cohen's, while Kaitlyn is back in Marissa's room, checking measurements and choosing paint colours. Looks like she's ready to take over her sister's legacy in a big way. She wants to rule Harbor next year.

Ryan and Marissa go to give Volchok the money he needs to leave town. They pawn a necklace that Julie gave Marissa for graduation and Ryan gives the cash to Volchok. Marissa drives up to get Ryan and Volchok runs up, pleading her to talk to him for a minute. Ryan jumps in the car and tells her to just drive. She peels out and Volchok is obviously extremely angry that she won't listen to him.

Sandy goes back to his old office to meet with the D.A. about what happened to the Newport Group office. He talks to a guy who took over for Sandy after he left and Sandy realizes just how much he misses his old work.

In Seth's room, Kirsten walks in and talks with Seth, saying that he doesn't have to apologize about the fire. Oddly, it may have been the best thing to happen to the family. She then shows him a letter that came in the mail from the school that he applied to in Rhode Island.

Later that day, the gang are getting ready to go to the last Harbor School party, when they suddenly change their minds. All they ever do at the parties is talk to each other. Marissa suddenly has an idea and tells them to follow her in Ryan's truck. She drives them straight to the new-and-improved model home (the one that was burnt down in the first season). It's empty at the moment as no one has moved in yet, so the four climb the gates and go have a swim in the pool and share one last laugh together afterward. They all hug as Marissa goes to change so Ryan can drive her to the airport.

Sandy comes home from talking to the D.A. and tells Kirsten that since they aren't laying any charges, the whole things will basically blow over. He also tells her how much he misses his old job and wants to go back.

Upstairs, Seth brings Summer into his room and has a present for her in a huge box. At first it looks like there's nothing inside, but then Summer climbs in and sees the acceptance letter Seth received earlier. His application was too late for the fall semester but he is asked to join the school in the second semester in January.

It's much later and darker outside as Ryan is driving with Marissa to the airport. They notice someone following very close behind them, honking their horn and flashing their highbeams. Suddenly, the car smashes into them and Marissa sees that it's Volchok driving (and drinking). He pulls up beside them and yells at Ryan to pull over. When Ryan doesn't, Volchok smashes into the side of Ryan's car repeatedly, until he actually rolls right off a cliff. The car goes end-over-end several times, then lands upside down. Ryan slowly wakes up and kicks a window out to get out. He sees a small fire and notices gas leaking. He knows he has to get Marissa out ASAP. He pulls her out and carries her away, just as the car explodes. He lays her down and tells her he's going to get help, but she tells him not to leave.

A few moments later, Marissa's eyes close and she stops breathing.

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