Captain Alatriste — Arturo Perez-Reverte

The first action-packed historical adventure in the internationally acclaimed Captain Alatriste series, featuring a Spanish soldier who lives as a swordsman-for-hire in 17th century Madrid. 

Needing gold to pay off his debts, Captain Alatriste and another hired blade are paid to ambush two travelers, stage a robbery, and give the travelers a fright. “No blood,” they are told.
Then a mysterious stranger enters to clarify the job: he increases the pay, and tells Alatriste that, instead, he must murder the two travelers. When the attack unfolds, Alatriste realizes that these aren't ordinary travelers, and what happens next is only the first in a riveting series of twists and turns, with implications that will reverberate throughout the courts of Europe...