Although described as a "mini-adventure" this is really a sandbox setting - albeit one based around a series of events rather than a specific locality. It's also worth noting that that, of the 65 pages, only 45 are actual content (indeed, many of the other 20 are entirely blank), and 4 of those are duplicate copies of player handouts in slightly different formats. The font size is quite large too, so, again, the book isn't as large as it appears at first glance. Still, for $5, the length is quite reasonable.
The book concerns the effects of a terrible plague on a fantasy city. The plague, of course, has to be immune to Cure Disease, and similar spells, or it frankly wouldn't be much of a threat. Which means that you would have to able to accept that such things are possible within your game world. The source of the plague is never explained, although there are some suggestions as to what it might be; however, the intent is clearly to bring some of the horror of real-world medieval plagues (the black death, the sweating sickness, and so on) to a game. In other words, its supposed to be about how the PCs react to something beyond their power to prevent, only to mitigate. This might not work well for all groups.
The content covers the course of the plague, including a whole series of events that occur throughout the city as it progresses. These include rioting, fires, unpopular civil ordinances, and, of course, the fact that the city is quarantined from the outside world. Although PCs might be helping to enforce, or possibly break, the quarantine, the main piece of "traditional" D&D action is the potential fight with some necromancers who briefly try to take advantage of the plague to unleash a horde of zombies from the mass graves. Like the other scenes in the book, though, this will need fleshing out by the GM, although stats are provided.
The book has new rules as well. Obviously, there's the plague itself, but there are also rules for mob action, rioting and urban conflagrations, as well as four new spells and a template for applying to undead. A major issue here may well be the plague rules; since it obviously can't be fought with magic, and has to be deadly to be scary, there's no obvious reason that the PCs won't catch it, with potentially disastrous consequences.
I like this book because it's original and different. It tries to bring something that medieval people were genuinely, and rightly, scared of, and tries to bring that same sense into a d20 fantasy setting. It sweeps the characters up in a horrific situation, giving them the opportunity to focus on the small aspects of life, presenting them with individual challenges framed against a larger, and more implacable, backdrop.
But it won't be to everyone's taste, and a GM may need to approach with caution.
[4 of 5 Stars!]