Brother Ptolemy makes one heck of a scary villain in my book. Not only is he powerful, but he's also anonymous — one Red Monk looks like every other Red Monk and nobody knows who or where Ptolemy may actually be. Plus, how do you kill something that's already dead? Add to that Ptolemy's high-ranking officials scattered throughout The Hidden Kingdom and you have a plague you must somehow stop at its source.
As a gamemaster (GM), there is more than enough in BP&THK to gradually introduce the monks and their nefarious goals to an existing campaign. Each chapter introduces tools and techniques for getting the player characters (PCs) involved and trying to get to the bottom of the mystery and misery as it unfolds.
"The Red Harvest" in chapter two starts things off with a disease. That leads to Corwyn in chapter three. There you get the sense that the gorgeous, crime-free city of Corwyn, is hiding a rotten core. In chapter four, you have a full blown adventure that pits the PCs against the hidden goals of the charitable and magnanimous Red Monks who may be holding a young woman against her will.
Now, I have to admit to not being familiar with any of the materials for fourth edition Dungeons & Dragons, but I will say that this adventure is extremely well laid out with enough flexibility to allow the PCs a chance to get into and out of many scrapes, close calls, and mob scenes. Want combat? It's in there. Want some great roleplaying opportunities? They're in there too. The book really seems to have a great balance.
The remaining chapters flesh out items, feats, rituals, and adventure hooks. My favorite item is a very low-magic item — the Beggar's Coin. This doesn't grant the owner any huge magical benefit, but with today's economy in the real world, I'm sure there are plenty of people who would want one. "When one of these coins is pressed tight into the palm of a hungry man, the hunger slips away; when these coins are dropped into the cup of a cold man, warmth slips over him." Sometimes the simplest things are the best.