I know that the Brother Cadfael books by Ellis Peters are enormously popular, as was the television series based on them which starred Derek Jacobi, but I've not read the books or seen the programmes. The entry on the writer in 100 Must-Read Historical Novels by Nick Rennison caught my eye, though:
"In a career that lasted more than fifty years, Edith Pargeter wrote dozens of crime novels, many of them set in the past ... some under pseudonyms, most notably Ellis Peters. Her greatest creation was the humane and sympathetic medieval monk Brother Cadfael who uses his knowledge of herbal medicines and his insights into human motivation to unravel the crimes that come regularly to trouble the town of Shrewsbury and its monastery .... A Morbid Taste for Bones immediately established the monk as one of the most intriguing historical detectives and his character grew ever more complex as the series continued...The herbalist monk has genuine depth [and] a personal history - he was a soldier in the crusades before he took the cowl in middle age - and his character has been shaped by a knowledge of the world outside the abbey walls. Many more medieval detectives have flitted through the pages of historical mysteries since A Morbid Taste for Bones was published but none has ever really matched him."
Have you read Ellis Peters?