Sister May was a female mouse Redwall Abbey Infirmary Keeper and one of the three residents who healed Stryk Redkite. Stryk showed her appreciation by saving her from an attack and naming her offspring May after the caretaker. She was known for being very clever.
Sister May also concocted a sleeping potion that was used to capture three magpies who were stealing from the orchard. Other notable acts included the biting the of the raven leader, General Ironbeak, and catching a grayling when Matthias was too weary.