Gladys Edson Locke (1887–1945) was an American writer best known for a series of atmospheric mystery novels published primarily in the 1920s and 1930s. She was the only child of Winfield Scott Locke, a merchant in women's undergarments, and Caroline Augusta Edson. Raised in the Dorchester neighborhood of Boston, Locke lived there for most of her life and remained unmarried.

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An accomplished student, Locke graduated from the Girls' Latin School in Boston in 1906 and continued her education at Boston University, earning an A.B. in 1910 and an A.M. in 1911. She later pursued Library Science at Simmons College, graduating in 1916. Between 1908 and 1916, she worked as a tutor and high school teacher, instructing students in Latin, French, Italian and English. In 1917, she began a long career as a cataloguer at the Boston Public Library. She was also active in her Unitarian church and a member of the Boston Society for Psychical Research.

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Locke published her first book, a biography of Queen Elizabeth I, in 1913. The following year, she released her first mystery novel, That Affair at Portishead Manor, and continued publishing in the genre. Her eleven novels often featured English settings and recurring characters such as Inspector Burton and Mercedes Quero. Her most famous novel, The Purple Mist (1924), is noted for its eerie atmosphere and the inclusion of seemingly supernatural elements later revealed to be rational in origin.

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Locke died in Boston in 1945.