Despite this short length, a lot happens. As was typical for science fiction stories of that era, particularly science fiction stories that were purposefully retreading the ground of science fiction from 50 years earlier, the plot zips forward at lightning speed. Major setbacks are set up, identified, worried about, and then resolved again in less than a dozen pages. Fox makes liberal use of deus ex machina to advance the plot; sometimes stuff happens for no good reason than because he said so.
The gist of it is that a certain type of bizarre jewel is being stolen across Llarn. Alan Morgan is called on to find out why, so he infiltrates the Thieves Guild, impersonating a famous thief Uthian the Unmatched. At this point, we get treated to the "sword & planet" M.O., that is, Fox has his character travel all over the place, visiting exotic locales. There's a kind of travelogue vibe to these types of stories; the action is interrupted occasionally for several paragraphs at a time as some item of local culture or technology or even history is explained, as if by a tour guide. This isn't necessarily meant to be a bad thing, though... as much as I almost hesitate to use the phrase, the point of this is to stroke our "sense of wonder" by showing us cheap exotica and thrills. Burroughs did it frequently, and most of his imitators do as well.
Fox has a little bit more rounded characters than is normal for this genre. Alan Morgan isn't just an everyman hero, he's kinda a dumb jock in a lot of ways, in over his head but for the author's intervention due to spectacular good luck. The women of Llarn are fairly interesting, showing hints of color and personality.
All in all, if you like this genre at all, I think you'll like the Llarn books. They have most of the same weaknesses that all of this genre seems to sport like a badge of honor, but luckily, the Llarn books also seem to have most of their strengths. And Fox has a bit of genuine cleverness here and there in how he exploits the formula. At times, I almost wonder if he's writing a subtle parody of the genre, but at other times I think that the parody is too subtle; more likely he's playing it straight.