Fic where Lucifer drugs Mammon with a long-form truth serum, as a punishment for continuously asking for money he doesn't need, and lying about the reasons. The punishments going well, Mammons humiliated, all of his future schemes have been revealed, and they've also gotten closer on account of Mammon not being able to lie about his feelings.
It's great! Everything's great, tied up with a bow.
Except, somehow, someway, the Anti Lucifer League (Satan and Belphegor) use their expert detective skills to uncover this new found flaw of Mammons (they live with them; Lucifer told them), and realize in short order that Lucifer has given a long-form truth serum to the one demon in the Devildom who knows all of his secrets










