“I was watching. I saw the whole thing. First it started falling over, then it fell over.”

The “beginning of the end” of The Simpsons isn’t in a wacky, over-the-top episode like The Principal and The Pauper. It’s more subtle. It’s the 23rd episode of the eight season: Homer’s Enemy.

Homer’s Enemy is just after In Marge We Trust and just before The Simpsons Spin-Off Showcase. That second episode is a good candidate too. It admits the show has run its course and it’s time to start thinking about the future. It’s this self-awareness that makes Homer’s Enemy the series’ turning point.

What’s the episode about? Well, it’s about Frank Grimes: a man who starts work at the power plant and becomes annoyed at Homer. It’s been said before, but Grimes is a proxy for the audience. He’s also a self-insertion for the writers themselves. They’ve created a monster and Grimes lets them vocalise their guilt about it.

Grimes points out Homer’s flaws, and how he’s never held accountable for them. He flags up that Homer lives in a huge house – despite “a lifetime of sloth and ignorance”. He’s the safety inspector for the power plant – yet a huge liability to those around him. Previously, these contradictions in the show went unspoken. As an audience, we’d bought into the notion that Homer’s lifestyle could sustain itself.

Grimes breaks this spell. And what happens to him? Like other detractors in the history of literature, he is condemned. The escapee from Plato’s Cave gets shunned by those he returns to. Meursault in Camus’ L’Etranger is sentenced for rejecting the morals of society. Likewise, Springfield won’t accept anyone who questions the status quo. Grimes dies in one of the most violent scenes in the show.

At his funeral, nobody shows remorse; Homer is even asleep. “Change the channel, Marge!” he blurts out. “That’s our Homer!” shouts Lenny. Like him, we can’t accept Homer changing now; not even when the absurd foundations of the show have been revealed. With Grimes’ grave, The Simpsons buries the last residues of its credulity.

And this is why it marks the beginning of the end. Once the genie is out of the bottle it can’t go back in. Like Bart’s factory in the episode’s subplot, The Simpsons has started to collapse in on itself.