If you're reading them in chronological order, rather than the order Cornwell wrote them in, this one has a greater intensity than the earlier Spanish books. Some enjoyable elements have returned. Sharpe is truly up against the career wall once more, his provisional appointment to Captain denied. He has a real love interest, his earlier dalliance with Spanish partisan Teresa Moreno taking a more serious turn. Harper's career is in jeopardy as well with the return of Sharpe's nemesis Obadiah Hakeswill, absent since the end of the third book, "Sharpe's Fortress" and the Indian battle of Gawilghur almost a decade before. All this fateful tension takes place against the backdrop of a monumental battle, the British assault on the heavily fortified city of Badajoz, held by the French and essential to any invasion of Spain. The heavily walled city is surrounded by a dozen strongpoints, water on two sides and modern fortifications elsewhere.
Losing his company to a well-born stranger with no experience, the now merely Lieutenant Sharpe must plot his future as the British wallow in the winter mud outside Badajoz waiting to breach its walls.
Cornwell's best writing in this series has been about 18th century siege warfare - the battering of the walls with artillery, use of the rubble as a ramp up to the broken part of the wall, and the hell the first invaders must go through to sieze the hole, after which they are invariably dead, or heroes. It is this and nothing but this, Sharpe thinks, that will win him back his captaincy.
Cornwell's writing of the storming of Badajoz, and the pillaging of it by British troops, has a special and fearful intensity to it, his best siege and fortress storming since the aforementioned Gawilghur in "Fortress". And Hakeswill - merely evil, malign and relentless in the first three books - is here not only that, but mad as well. At times he sounds like Tolkien's Gollum, talking to ... well, you'll see.
In the order that Cornwell originally wrote them, this is the first time he does a real siege and the first time he writes Hakeswill. Both come horribly alive. This book is short and bowstring-taut. Not a word is wasted.