Monk's-Hood by Ellis Peters

The provided text details a complex narrative centered around Brother Cadfael, a Benedictine monk with an unexpected past, as he navigates a murder investigation and abbey politics. Abbot Heribert's unexpected summons to a legatine council in London throws the abbey into disarray, suspending his authority and delaying critical agreements, including a house transfer to Master Bonel. This uncertainty allows Prior Robert to prematurely assume power, moving into the abbot's lodging and displaying his ambition. The sudden death of Master Bonel from poisoning leads to suspicion falling on his stepson, Edwin Gurney, due to a contentious inheritance and his flight from the scene. Brother Cadfael, reconnecting with Richildis, Edwin's mother and Cadfael's former fiancée, is compelled to investigate, using his knowledge of herbs to identify the poison and uncover the true circumstances of Bonel's death. The investigation eventually reveals Meurig, Bonel's Welsh son, as the murderer, driven by a desperate desire to secure his ancestral land, which would have been lost had the abbey charter been sealed. Ultimately, Cadfael secures Edwin's freedom and ensures Meurig's escape, while Abbot Heribert returns, disappointing Prior Robert's aspirations.