Affaire (1935) was her third film with Powell. She followed it with She Knew What She Wanted (1936), Crown v. Stevens (1936) (directed by Powell), Crime Over London (1936), Pearls Bring Tears (1937), Action for Slander (1937), and Paradise for Two (1937). Withers had the lead in You're the Doctor (1938) and was back to support for Kate Plus Ten (1938). Her best-known work of the period was as one of Margaret Lockwood's friends in Alfred Hitchcock's The Lady Vanishes (1938). She continued in support roles in Paid in Error (1938) and Strange Boarders (1938). She was in a Will Hay film Convict 99 (1938) and supported Jack Buchanan in The Gang's All Here (1939). Then she appeared in crime films Murder in Soho (1939) and Dead Men are Dangerous (1939). She supported George Formby in Trouble Brewing (1939) and Tommy Trinder in She Couldn't Say No (1939). She was in a Robert Montgomery film Busman's Honeymoon (1939) and was reunited with Buchanan in Bulldog Sees It Through (1940). She was still supporting comics in Back-Room Boy (1942) with Arthur Askey. Rising fame Among her successes of the 1940s, and a departure from her previous roles, was the Powell and Pressburger film One of Our Aircraft Is Missing (1942), a topical World War II drama, in which she played a Dutch resistance fighter who helps British airmen return to safety from behind enemy lines. Powell and Pressburger then used her in a film they produced but did not direct, The Silver Fleet (1943). She played Helen, a significant second lead in the Clive Book-directed 1944 comedy On Approval. Withers was in They Came to a City (1945), directed by Basil Dearden, and was one of several stars in Dead of Night (1945). She was given a star part in Pink String and Sealing Wax (1945). It was well received, and Withers was given the title role in The Loves of Joanna Godden (1947), which was a hit. In the cast was actor John McCallum, whom Withers later married. They remained married until McCallum died in 2010. Withers then starred in It Always Rains on Sunday (1948), which was one of the biggest hits of the year. In 1948, British exhibitors voted her the 8th most popular British star in the country. Three comedies followed: the hugely popular Miranda (1948), with McCallum, and Once Upon a Dream (1949) and Traveller's Joy