The Wayward Alliance - The Sir Law Kintour Mysteries, #1

Sir Law Kintour has returned from the war in France injured, broke, and in need of a patron. In desperation, he reluctantly accepts a commission to find a nobleman's runaway wife. He enlists the help of a fellow Scot with whom he escaped after their defeat at the Battle of Verneuil. But his friend is murdered, and Law discovers he has been lied to. As the murders continue to mount, powerful interests come into play.
When the Sheriff of Perth considers him a convenient scapegoat, it gives Law no choice but to untangle the lies and find the killer or hang for the murders.(Originally publised as 'The Templar's Cross)