Essentially the local mage is looking for a certain rare spell, which was known to be in the spellbook of a magic-user named Thurindisar. While most mages seem to be make do with towers, Thurindisar wasn't satisfied with that and lived on the Moon. So the PCs are hired to go there, sent by a magical telescope, to recover the spell.
The Moon of the module is sort of like our Moon. Airless, so the PCs also get some magic to help them survive. But the module Moon also is inhabited by friendly moon people and a small number of moon monsters that will get in their way as they travel to the library. Things really get crazy when they actually reach Thurindisar's home.
Basically someone else is looking for that very same spell the PCs were sent after. Evil aliens which bear some similarity to Daleks, at least in personality (they actually look more like flying toasters) and their hired thugs, who aren't too bright but have rayguns. They also encounter a friendly library robot and what is essentially a Jedi, a "Paladin of Space" which is apparently one of the authors rule supplements (but is summed up in the character description).
|Not the Dalek style alien, but their guard robot|
The author is also an artist so there are quite a few illustrations, the quality of which ranges from passable to pretty good. As with his other modules, he's included battlemaps and counters for playing this via a virtual table top.
Much to my delight, the default settings of the PDF are "Single Page" and "Fit Height" so I don't have to spend 2 seconds changing them to that every time I open it. This is a minor thing, but I've never understood why you don't see more of it.
My favorite part of the OSR are the "do it yourself" style modules from one (or two) people, as opposed to the more professional stuff or Kickstarter projects. There's a fair amount of "meh" in those, but it's good, honest "meh" that someone worked hard for just for the love it, not for the money. And occasionally you end up with a real gem, like this, The Lunar Library of Thurindisar.