In this episode, Bart is diagnosed with ADD. So he needs to take an experimental drug called Focusyn. He takes it and at first, changes, becomes smarter, stuff like that.
But later he becomes a conspiracy theorist. He goes insane and goes into the Army Base to steal a tank and shoot it into the sky. After he does so, Springfield citizens see that baseball players have been spying on them for reasons unknown.
At the end, Bart is no longer on Focusyn, and all else is normal.
A wacky episode with a wacky third act, but it still has plenty enough humor for me to overlook this. Well, for the most part