If you have finished Ellis Peter's Brother Cadfael series and are looking for something comparable in quality in roughly the same time period, then read about Owen Archer, a creation of Candace Robb. Also a former soldier, and now an apprentice herbalist (sound familiar?), Captain Archer works part time as a spy and investigator for the Archbishop of Canterbury. Unlike Brother Cadfeal, Owen is married and has a daughter.
All are good, but, IMHO, book four in this series was the best yet.
March 1367. King Edward is impatient. He wants his privy councillor, William of Wykeham, confirmed as Biship of Winchester, but Pope Urban V is stalling, deterred by the man's wealth and political ambition. Owen Archer heads a deputation from York to Fountains Abbey to win support for Wykerham from the powerful Cistercian abbots. Trouble erupts as a friar and Ned Townley vanish, following news of a murder at Windsor. The King's mistress, Alice Perrers, becomes involved.
Medieval detective Owen Archer finds himself solving a murder involving the King's mistress, Alice Perrers, ever a dangerous enemy.