One of Our Spies Is Missing is the 1966 feature-length film version of The Man from U.N.C.L.E.'s second season two-part episode "The Bridge of Lions Affair". The episodes were originally broadcast in the United States on February 4, 1966 and February 11, 1966 on NBC. The film is directed by E. Darrell Hallenbeck and written by Howard Rodman. It, as does the television series, stars Robert Vaughn and David McCallum. It is the fourth such feature film that used as its basis a reedited version of one or more episodes from the series. However, this film, and the episodes it draws from, represents the only instance where a Man from U.N.C.L.E. story is derived from an existing novel: The Bridge of Lions (1963) by Henry Slesar.

David Keith McCallum was a Scottish actor and musician. He gained wide recognition in the 1960s for playing secret agent Illya Kuryakin in the television series The Man from U.N.C.L.E. His other notable television roles include Simon Carter in Colditz (1972–1974) and Steel in Sapphire & Steel (1979–1982). Beginning in 2003, McCallum gained renewed international popularity for his role as NCIS medical examiner Dr. Donald "Ducky" Mallard in the American television series NCIS, which he played for 20 seasons until his death. On film, McCallum notably appeared in The Great Escape (1963), and as Judas Iscariot in The Greatest Story Ever Told (1965).