Sharpe's Company (Bernard Cornwell, 1982) was my airplane book for our journey from Seattle to Tulsa yesterday. It's one of the earliest Sharpe books in terms of publication, and it's a solid, page-turning entry, though Triumph, Trafalgar, and Gold remain my favorites. It covers the early 1812 sieges and storming of Ciudad Rodriguez and Badajoz, two key fortresses on the Portuguese-Spanish frontier. The British needed both cities to advance into Spain and stay there, and they paid for them dearly, particularly at Badajoz, in terms of casualties--some of the hardest-hit regiments had 25% casualty rates.
I read Company with particular interest because I used Badajoz as part of the setting for The Sergeant's Lady. I don't think my research steered me wrong--it plays a very different role in my plot and takes up a MUCH smaller portion of the page count, but it reads like the same battle.