M5: Talons of Night
M5: Talons of Night is the last Moldvay-Mentzer run at Epic play, by way of the "Master's" line. Here TSR let an illustrator write the text, one Paul Jaquays. He embarrasses the other Master writers by being competent and original.
Here concludes the M1, M2, M3 (but not M4) attempts of Alphaks to gain revenge on Alphatia by way of catspaw Thyatis. After M2's rehash, everyone is damn tired of replaying the War Machine on Norwold's soil, so it's off to the Isle of Dawn... but Jaquays isn't willing to rehash that plot here, either. Instead the emperor of Thyatis and the empress of Alphatia have been dragged into some other plane.
The party comes to Cairo I mean, Edairo. It's run by parody "Pharoahs" (spelling not being among Jaquays' talents), who've let the kingdom to seed like... er, the real Pharaohs of the later Ramessides. The library burns down because this generation can't read anymore and don't give a shit, and also because there's only so much expository lore a DM is willing to dump on a party at one time or that an author was willing to sketch out in a single small module likely to be the last chance anyone would get. Based on what the party finds, it's off on a multiplanar Descent Into The Underworld, here planes under the shadow of The Sphere of Death.
First is the plane of Thorn, a sort of burr on the side of Yggdrasil World-Ash; then the plane of Chasm, the most atmospheric of the settings here which plays like AD&D Pandemonium. Time flows differently on these planes, and the Sphere's necrotic energies might also turn the party into deadites if they're not fast and careful enough. The two emperors are beyond Chasm's Tower of Night on the Isle of Night, a scaled-down model of the Isle of Dawn, where they've learnt to live together, inasmuch as anything can live on the Sphere of Death.
This one has the distinction of laying out the lore behind Thyatis, and sets up a gazetteer for the central part of the Isle of Dawn. That will be fleshed out in Dawn of the Emperors. Also Mongoose's Classic Play: The Book of the Planes will (2004) feature a Chasm plane with some similarities with this one's.