He appeared in the biographical epic film "John Paul Jones" (1959), in which Robert Stack played the title role of the American naval fighter in the American Revolutionary War. Cushing became very ill with dysentery during filming and lost a considerable amount of weight as a result. Cushing played Robert Knox in "The Flesh and the Fiends" (1960), based on the true story of the doctor who purchased human corpses for research from the serial killer duo Burke and Hare. Cushing had previously stated Knox was one of his role models in developing his portrayal of Baron Frankenstein. The film was called "Mania" in its American release. Cushing appeared in several films released in 1961, including "Fury at Smugglers' Bay", an adventure film about pirates scavenging ships off the English coastline; "The Hellfire Club", where he played a lawyer helping a young man expose a cult; and "The Naked Edge", a British-American thriller about a woman who suspects her husband framed another man for murder. The latter film starred Deborah Kerr, Cushing's co-star from "The End of the Affair", and Gary Cooper, one of Cushing's favourite actors. In 1965, Cushing appeared in the Ben Travers farce play "Thark" at Westminster's Garrick Theatre. It was his final stage performance for a decade, but he continued to stay active in film and television during this period.