Sebastian is a 1968 colour film by director David Greene and producers Michael Powell, Herbert Brodkin and Gerry Fisher.

The film stars Dirk Bogarde as an Oxford don turned cryptographer, Susannah York as a member of his decoding team and John Gielgud as the Head of Intelligence. Among the many striking features of this underrated though cult film are: the modernity of the cinematics of London, foregrounding the contrast of new and more traditional streetscapes and architectural values, and at the same time, the lifestyles of academe and those of 'swinging London'; the confrontative style of the representation of male-female relationships; the linked themes of the psychology and science of interpretation, as the hero and heroine struggle with puzzles in cryptography and problems in human communication. A dazzling composite metaphor forms the resolution when the hero hears in his newly-encountered baby's rattle the sound-pattern which will lead him to solve the decoding problem which is threatening national security - a problem itself treated in a composite stylistics of classic thriller on the one hand, and more complex approach to ethical-political beliefs on the other.

A British mathematician, working on code decryption, unexpectedly falls in love with another decrypter. This leads them to a complicated intrigue within the codebreakers. Written by Steve Crook