As a Ziegfeld Follies girl and film actress, Justine Johnstone (1895-1982) was celebrated as ""the most beautiful woman in the world."" Her career took an unexpected turn when she abruptly retired from acting at 31. For the remainder of her life, she was a cutting-edge pathologist. Her research at Columbia University contributed to the pre-penicillin treatment of syphilis and she participated in the development of early cancer treatments at Caltech. The first full-length biography of Johnstone chronicles her extraordinary success in two male-dominated fields-show business and medical science.