Cassia Joy Cowley ONZ DCNZM OBE (née Summers; born 7 August 1936) is a New Zealand author best known for her children's fiction, including the popular series of books Mrs. Wishy-Washy. She started out writing novels for adults, and her first book, Nest in a Falling Tree (1967), was adapted for the screen by Roald Dahl. It became the 1971 film The Night Digger. Following its success in the United States, Cowley wrote several other novels, including Man of Straw (1972), Of Men and Angels (1972), The Mandrake Root (1975), and The Growing Season (1979). Typical themes of these works were marital infidelity, mental illness, and death, as experienced within families. Cowley has also published several collections of short stories, including Two of a Kind (1984) and Heart Attack and Other Stories