21 Days, also known as 21 Days Together in the U.S., is a 1940 British drama film based on the short play The First and the Last by John Galsworthy. It was directed by Basil Dean and stars Vivien Leigh, Laurence Olivier and Leslie Banks. It was filmed in black and white. A man kills his lover's husband in self-defence and hides the body rather than turn himself in to the police. Then another man is arrested for murder.