The story begins on familiar ground as we walk through the events of the Hunger Games themselves (as we did in books I and II) but where those were smooth running affairs, it is apparent that at this early date, they were still working out the kinks. In striking contrast, the body count has racked up long before the Games even start.
Snow is a student at the Academy and in a novel new twist this year the students have been enlisted to "mentor" the tributes. Snow gets assigned to the female tribute from District 12, Lucy Gray. She's a musician and and a member of a wandering troupe of romani-like entertainers called the Covey. Like a gypsy, she flits around in colorful skirts and charms the people around her (including Grey himself) which proves decisive in her ability to stay alive and defeat much more able opponents. But there is more than charm at play. They have a mutual shared interest in her staying alive. Her success in the Games will help Snow get a college scholarship he desperately needs.
That works fine during the Games, but when things go awry and the story shifts to District 12, their roles change. The mutual interest persist, but there is suspicion and distrust and Snow doesn't know if he can trust her anymore. But in all honesty, could he ever trust her?
There are several things that make this a very different sort of story. One obvious difference is the point of view. In the trilogy, we are seeing the world through the eyes of Katniss and her rebellion against the Capital District. Here, the story is told through Snow and life in the Capital is nowhere near as easy as we have grown used to it. Some of that is because the Capital is still rebuilding from after the war, but Collins is also showing us that even those who benefit from the power structure suffer.
This is the origin story of a tyrant. While Katniss was heroic and fighting a good fight through most of the story, Snow is a troubling protagonist. Some of his ideas (in particular his obsession with order and his selfishness) are odious. One starts feeling uneasy when the book pushes us to root for the oppressors and we hope that the rebels get caught and killed.
An interesting message to explore in a YA book, but what about the story itself? It's long and meanders a lot. Once the Games are over, the story truly drifts away from its focus, but it does eventually come back together in the end, in a rushed finale that solves problems by largely killing off characters (an approach also found in Mockingjay). This is a less accessible story. It is hard to imagine someone picking up this book without already having been drawn in by the trilogy. In sum, not just a prequel but an ambitious political critique that is fated to be read by fans looking for some Katniss magic and disappointed to find only gloomy portents of the things to come.