The pivot point of this book is the battle of Cannae, in which Hannibal and his Carthaginian forces defeated a larger Roman army, in the process killing off huge numbers of Roman troops. But the book is about more. It provides the earlier context, the first war between Rome and Carthage, the tensions remaining between the two powers, the factors leading to the second Punic War (Rome versus Carthage), and so on. The book ends by noting how for the past 100 years, a number of generals have expressed a desire to repeat the Cannae model, hoping to annihilate the opponents.
The book is, of necessity, speculative, since there is not an abundance of good information on the battle and the context in which it occurred. Indeed, one map of the battlefield, on page 147, indicates that it is not clear exactly where the battlefield was located. The book does a nice job identifying and discussing key leaders among Romans and Carthaginians. Exotic issues are explored nicely, such as the pluses and minuses of battle elephants. Or the nature of the naval war between Rome and Carthage in the First Punic War.
The book is well written, though, and provides a useful exploration of the battle and its subsequent effects.