Burton Guster is freaking out.
This isn't really all that unusual. Burton Guster has demanding parents, high expectations of himself, and Shawn Spencer for a best friend. Having Shawn as a best friend is great (after all, if it weren't for him, people might actually call Gus Burton) but it is very stressful.
Gus has to give a speech today, at his graduation, but that's not why he's freaking out.
That is unusual. Public speaking is one of Gus's biggest fears, right behind being falsely imprisoned.
What Gus is worried about is Shawn.
As already mentioned, that isn't that weird. Shawn is eccentric, and he tends to do very stupid things so that he controls his dad's dissappointment. It makes Gus angry sometimes, that Mr. Spencer is never proud of Shawn. Shawn is absolutely brilliant, much smarter than Gus could ever hope to be, but he hasn't really tried since he realized his dad would always put his job first.
Shawn being who he is, Gus knows other people are probably worried about him too. The principal, specifically, probably worries that he's plotting some prank for graduation, but Gus knows Shawn wouldn't do anything during Gus's speech, so he doesn't see that as a problem.
A lot of people don't entirely understand why Gus is friends with Shawn, but they don't know the real Shawn. They only see his eccentric, slightly ridiculous cover. Underneath that, though, Shawn is the most perceptive person o the planet, and a good friend. And really, until you've been told not to be the least attractive member of the Backstreet Boys, you haven't lived.
Gus's worry is that Shawn is about three steps from the edge of a cliff, or more literally, about two arguments with his dad and one more absence by his mom from doing something immensely, potentially irredeemably stupid.
It's hard to believe that Shawn, who notices everything, was completely blindsided by his parents' divorce, but it's true. Mrs. Spencer left, but Shawn blames his dad. Gus knows it's not Mr. Spencer's fault, but he can't bring himself to tell Shawn and ruin his faith in his mom. He needs at least one parent he isn't furious with.
Speaking of Shawn, he's not here yet and graduation is going to start any minute. Gus wishes he could be sure of Shawn showing up, but Shawn is completely unpredictable to most people, and he still manages to surprise even Gus occasionally.
For example, Shawn's dad thinks he always knows what Shawn's going to do – specifically, exactly the opposite of what Mr. Spencer wants. On the other hand, Mr. Spencer may be realizing he doesn't know Shawn as well as he thinks. After all, he never thought Shawn could be as quiet as he's been since Mr. Spencer arrested him two weeks ago. The fact that Shawn had to stay with his dad after that ticks Gus off, but the Spencer men have that stupid "don't call mom" policy. Gus hadn't understood that when they were younger. His mother would have been furious if they didn't call her for little stuff, let alone gunshot wounds and nearly fatal cases of pnuemonia, and she would have rushed home immediately when the call came in. He's realized lately that Mrs. Spencer is actually happier not knowing. This is why Gus is actually angrier at Mrs. Spencer than Mr. Spencer. Mr. Spencer has at least always been absolutely involved with Shawn, even if he goes about it wrong, while she simply doesn't care, and Shawn wants her to so, so much.
"Line up graduates! It's time for the march!" That's the principal. Shawn's not here yet, and he's out of time. Hopefully he won't be too late, and he can slide in unobtrusively.
Gus knows better, really. Anything that's grounds for another lecture isn't going to go unnoticed by Mr. Spencer. He sees every bad thing that Shawn does, but none of the good ones.
Gus marches in to "Pomp and Circumstance", right at the front of his class, since that's where the valedictorian belongs. He wouldn't be valedictorian if Shawn bothered to try, but as it is, it's his spot. He searches for any sign of Shawn sliding into place at the last minute, and catches Mrs. Spencer arriving late instead. Mr. Spencer turns to glare at her, she glares right back, and Gus just hopes they aren't going to start a fight in the middle of the ceremony.
Mr. Spencer doesn't seem to have noticed Shawn's absence. He kind of wonders about that, how Shawn got away from his dad today, but figures Shawn can get away with just about anything with anyone else, his dad was bound to slip up sometime. This just goes to show, though, exactly how Shawn can fall by the wayside in the Spencer household. Gus can't even count the number of times that Shawn snuck out to stay at his house when his parents were fighting, and then snuck back in the next morning without his parents even noticing. Shawn can climb up and down the tree by his bedroom window in about three seconds with all the practice he's had.
Graduation flies by. Gus isn't paying a whole lot of attention because Shawn still isn't here. His speech goes off without a hitch, probably because he's too distracted to be nervous. He gets his diploma, still looking around, but they reach S for Spencer and no one answers that call. The principal looks surprised, apparently thinking even Shawn wouldn't miss graduation, and Mr. and Mrs. Spencer look baffled, catching his eye. He just shakes his head. He doesn't know where Shawn is.
It turns out Gus wasn't freaking out before. NOW he is freaking out. Where is Shawn? He could be hurt. Then again, he could just be asleep. But if Gus had a third hand, it would be that Shawn might be doing that irredeemably stupid thing he was worried about earlier.
Gus tries to do the normal post graduation stuff. He hugs some friends, high fives some others, takes the requisite pictures with his parents. Finally, they head home, to set up for the barbeque they're putting on for his family, and his dad checks the mailbox on the way past, just like always. He comes up with a folded piece of paper, which reads "Gus, buddy, was the speech totally awesome? I knew it would be, Mr. Most Likely to Succeed. Sorry I wasn't there to hear it, but I had to go. Don't let my dad guilt you. Just remember, you actually didn't know anything this time, and you couldn't have stopped me. I'll send a postcard or something. You're the best friend a guy could ask for. – Shawn "
It's really just like Shawn, to disappear without any warning, explanation, or apology. Of course, the fact that he gave no warning allows Gus to honestly say he doesn't know where he is. He hopes he'll be okay, and that he'll come back eventually.
Weeks later, Gus gets a postcard in the mail. Shawn says he's fine. He says it in true Shawn fashion, with too many quips, and next to no real information, but it's there.