[1] Larry Darrant, the black sheep of his family, returns home to London from an unsuccessful business venture in Kenya and embarks on an affair with a married woman, Wanda.

When Wanda's long-absent Russian husband Henry appears, he tries to extort money from the couple and threatens Larry at knifepoint when he refuses to pay.

Producer Alexander Korda intended 21 Days as a star vehicle for Vivien Leigh, but his constant interference caused great problems on the set.

He rearranged shooting schedules and added a sequence, and director Basil Dean reportedly never viewed a rough cut or the finished product.

Following Leigh's star turn with her performance as Scarlett O'Hara in Gone with the Wind (1939), Korda shelved 21 Days for two years before releasing it to Columbia Pictures.