Although the story is highly fictionalised, the process of encrypting German messages during World War II and decrypting them with the Enigma is discussed in detail, and the historical event of the Katyn massacre is highlighted. It was the last film scored by John Barry.
The story, loosely based on actual events, takes place in March 1943, when the Second World War was at its height. The cryptanalysts at Bletchley Park, Buckinghamshire, have a problem: the Nazi U-boats have changed one of their code reference books used for Enigma machine ciphers, leading to a blackout in the flow of vital naval signals intelligence. The British cryptanalysts have cracked the "Shark" cipher once before, and they need to do it again in order to keep track of U-boat locations.
The film begins with Tom Jericho returning to Bletchley after a month recovering from a nervous breakdown brought on by his failed love affair with a coworker named Claire Romilly. Jericho immediately seeks to see her again and finds that she mysteriously disappeared a few days earlier. He enlists the help of Claire's housemate, Hester Wallace, to follow the trail of clues and learn what has happened to Claire.
Mr. Jericho and Miss Wallace, as they formally address each other, work to decipher intercepts stolen by Claire and determine why she took them. Jericho is closely watched by an MI5 agent, Wigram (Jeremy Northam), who plays cat and mouse with him throughout the film. Meanwhile, U-boats are closing in on a convoy of thirty seven ships from America, giving the code-breakers less than four days to find a solution to reading the changed Shark cipher.
But someone else at Bletchley has a personal interest in the stolen interceps, and may be responsible for Claire's disappearance.Dougray Scott - Tom Jericho
Kate Winslet - Hester Wallace
Saffron Burrows - Claire Romilly
Jeremy Northam - Mr Wigram
Nikolaj Coster-Waldau - Jozef 'Puck' Pukowski
Tom Hollander - Guy Logie
Donald Sumpter - Leveret
Matthew Macfadyen - Cave
Robert Pugh - Skynner
Corin Redgrave - Admiral Trowbridge
Nicholas Rowe - Villiers
Edward Hardwicke - Heaviside
The film was shot on location in England, Scotland and the Netherlands, with Bletchley Park mansion substituted by Chicheley Hall. Other locations include the Great Central Railway, Loughborough and Tigh Beg Croft, near Oban, Scotland. Interiors were filmed at Elstree Film Studios.
The film was produced by Mick Jagger of the Rolling Stones. Jagger makes a cameo appearance as an RAF officer at a dance. He also lent the film's design department a four-rotor Enigma encoding machine he owned to ensure the historical accuracy of one of the props. The festivities around the London premiere of the film are shown in the 2001 documentary Being Mick.
Critical reviews were largely positive, but there was criticism of the largely fictional storyline, which neither mentions the real codebreaker, Alan Turing, nor gives due credit to the Polish cryptanalysis foundation, the Biuro Szyfrów (Cipher Bureau). The film holds a 'fresh' 72% rating on review aggregate Rotten Tomatoes, with the consensus reading, 'The well-crafted, twist-filled Enigma is a thinking person's spy thriller.' Joe Leydon of Variety compared the film to works by Alfred Hitchcock, and remarked that, 'Overall, "Enigma" plays fair and square while generating suspense with its twisty plot. And while it requires a generous suspension of disbelief to accept a few action-hero gestures by the deeply troubled Jericho, Scott is persuasive and compelling enough as his complex character to drive the narrative.'
Roger Ebert of the Chicago Sun-Times gave the film three stars and said, 'What I like about the movie is its combination of suspense and intelligence. If it does not quite explain exactly how decryption works (how could it?), it at least gives us a good idea of how decrypters work, and we understand how crucial Bletchley was—so crucial its existence was kept a secret for 30 years.' On the other end, Owen Gleiberman of Entertainment Weekly was far less impressed, saying, 'The legend of how the British cracked the almighty Enigma must have sounded, on paper, like a nifty mathematical thriller—a historic WarGames set at the formative moment of the computer age. On screen, however, Enigma plays as if the scriptwriter, Tom Stoppard, and the director, Michael Apted, were themselves cryptographers; they seem to be making hunt-and-peck stabs at how to translate a tale of arcane numeric formulas into drama.'
The film and, by association, the book have attracted criticism for their portrayal of the Polish role in Enigma decryption. The historian Norman Davies argues that in the film the fictitious traitor turns out to be Polish, but only slight mention is made of the contributions of prewar Polish Cipher Bureau cryptologists to Allied Enigma decryption efforts, but historically, the only known traitor active at Bletchley Park was British spy John Cairncross, who passed crucial secrets to the Soviet Union.