Alfred Hitchcock's 1935 thriller follows the getaway of Richard Hannay (Robert Donat), a man accused of murder. While Hannay must outsmart the police in his escape, he also finds himself sought by the actual assassins, who believe he is witness to a secret mathematical expression. The formula that everyone must know is a means of rendering an engine silent, finally divulged as “1 — (1/R)γ, where R represents the ratio of compression and gamma…” along with some fragments of the remainder of the formula. As is usual for a Hitchcock film, the driving force of the plot is trivial to the viewer. The classified expression, which every character cares about, is Hitchcock's trademark MacGuffin, a means to an end.
Apparently, math has its sinister side, for its secrets are guarded not only by professors and researchers, but political assassins. Hitchcock would continue this idea of top-secret math in his 1966 film Torn Curtain.