Homer wakes up to a world where everyone and everything is made up of bricks of Legos. As he picks up a playset for Lisa, he suddenly has a flash of an alternate reality. Eventually, he discovers that the entire Lego Springfield is a hallucination he created after Lisa rejected him to spend time with her new older friends. To deal with the emotional devastation of losing Lisa when they were just getting close, he goes the Springfield Lego competition without Lisa.
Homer is knocked out by Comic Book Guys large model of The Survival Games heroine, but, in his hallucination, he realizes he doesn't want to wake up to reality. Homer spends time with Lisa in a world where she can't grow up. Over time, he eventually figures out that it's good for the kids to grow up and move on even if it hurts his feelings.