In the short story The Apples of the Hesperides, Kate Casey was the daughter of the Liverpool cat-burglar Patrick Casey.
Unlike her father, Kate took after her mother and was highly religious. She entered the Convent of St Mary and All Angels at Inishgowlen in Western Ireland and became a nun by the name of Sister Mary Ursula.
Poirot travelled to Ireland in an attempt to meet her as part of his effort to recover a golden goblet which Kate's father had stolen. He hoped she might cast some light on where her father might have hidden the item. However, Kate had died at the convent about two months earlier.