Unwillingly, Sharpe takes over the task of drilling the Real Compania Irlandesa, a Regiment of untrained Spanish soldiers with Irish ancestors, who guarded until now the (empty) palace of the Spanish kings in Madrid.
In a lonely decayed border fortress in the hills Sharpe and the Chosen men do their best. Nevertheless, the soldiers desert in big numbers. Only when learning, that the French Major Loup and his "wolf brigade" slaughter all deserters, the soldiers stay under compulsion in the crumbling fortress.
Finally, it comes to battle, and the Irish company unexpectedly proves itself in the fight against the cruel French "wolves"...