Plot

A young genius frantically races against time to crack an enemy code and solve the mystery surrounding the woman he loves.

During the heart of World War II, in March of 1943, cryptoanalysts at Britain's code-breaking center have discovered to their horror that Nazi U-boats have changed their Enigma Code. Authorities enlist the help of a brilliant young man named Tom Jericho to help them break the code again. The possibility of a spy within the British code-breakers' ranks looms and Tom's love, Claire, has disappeared. To solve the mysteries, Tom recruits Claire's best friend, Hester Wallace. In investigating Claire's personal life, the pair discovers personal and international betrayals.—Anna <dimenxia@yahoo.com>

During the Second World War, a team of genius is put together near to London to study means of breaking the German code used in the communication. Tom Jericho broke this code in the past and had a break-down. Now his passion Claire Romilly is missing and the British counter-espionage system believes she is a German spy. Tom becomes closer the Claire's best girl-friend Hester Wallace and together they try to resolve the mystery of the disappearance of Claire in an war environment surrounded by suspicion and stress.—Claudio Carvalho, Rio de Janeiro, Brazil

During World War Two, the British authorities discover that Nazi U-boats have unexpectedly changed the code of their Enigma machines - thus endangering the lives of thousands of Allied sailors. They enlist the help of Tom Jericho (Scott), a brilliant young code breaker. But Tom also needs to solve the mystery surrounding the woman (Winslet) he loves, who is suspected of being a spy.

The story, loosely based on actual events, takes place in March 1943, when the Second World War was at its height. The crypt-analysts 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 crypt-analysts 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 (Dougray Scott) returning to Bletchley after a month recovering from a nervous breakdown brought on by his failed love affair with a coworker named Claire Romilly (Saffron Burrows). Skynner (Robert Pugh) is the head of the facility and dislikes Jericho. Guy Logie (Tom Hollander) is a fellow crypt-analyst and a friend of Jericho, so is Jozef 'Puck' Pukowski (Nikolaj Coster-Waldau). Admiral Trowbridge (Corin Redgrave) is threatening to take over the crypt-analyst program and Skynner is in a state of panic.

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 (Kate Winslet), to follow the trail of clues and learn what has happened to Claire.

Meanwhile, U-boats are closing in on a convoy of thirty-seven ships from America (there were a total of 141 ships sailed from US in 3 convoys), giving the code-breakers less than four days to find a solution to reading the changed Shark cipher. Jericho explains to the Navy that the shark enigma machine gives 4 billion, billion combinations to turn plain text into undecipherable text. even with the same settings, one text never comes out the same way when encrypted. The Brits have the enigma machine, but not a reference code to decipher the enigma settings for that day. When the crypt-analyst team got the weather code book the last time, they broke the code in 10 months.

Cave (Matthew Macfadyen) is Naval intelligence and befriends Jericho. He says he knows that Jericho broke the enigma cipher using the German code book used for transmitting weather codes. Jericho searches Claire's apartment, and under a floorboard he finds stolen German transmissions, that could have helped decipher the new shark enigma codes. Jericho beseeches Hester to reveal where Claire is hiding. The 4 messages were sent hours before (in 5 letter crypts, rather than the usual 4 letter crypts sent by Germans) the Germans switched to the new codes. They all come from the same source ADUADU.

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). Wigram questions Jericho on whether he went mad due to Claire and he says that Claire was not his girlfriend. Jericho admits to Wigram that he and Claire had sex and he fought with Claire after she went through her stuff and tried to keep his papers.

When Wigram leaves, Jericho burns the stolen transmissions he recovered from Claire's room and remembers that he revealed every official secret to Claire about his crypt-analytic work when Claire stopped speaking to him. Hester tells Jericho that ADU stands for a German signals unit based in the Ukraine. They wonder why Claire stole those 4 encrypted messages. Jericho knows that Claire would need a Typex machine along with the enigma settings for that day to read the messages. Hester knows that ADU had sent 7 more messages previously, which were decoded and filed (filing decoded messages was Claire's main job). Hester references the file and finds that the 7 decoded messages are missing.

Cave calls a meeting and says German U boats in the North Atlantic have gone into radio silence. this mean they are preparing for an attack. The first one to sight a U boat will break the radio silence by transmitting contact and location using the short signal code-book (which Brits have a copy of). The Germans changed the weather codes, but not the short signal code book. But the plan depends on the U boats finding the convoy and that means the sacrifice of many lives. Meanwhile Hester figures out that all received copies of the transmission are kept at the receiving radio station outside of town and then sent to Bletchley for crypt-analyst work. Hence while the 7 intercepted and filed messages are removed from the Bletchley filing system, it is possible that they are still available in the receiving filing location. Hester gets Jericho to bring the Enigma machine along. They steal the 7 missing messages from ADU (plus the 4 that Claire stole, and Jericho burnt) and also find that ADU has still been transmitting, but the receiving station is under orders not to record ADU's messages anymore.

Hester and Jericho manage to use the enigma machine to decode 1 message partially, only to get gibberish again (making them think that maybe the settings were wrong), before they are intercepted by Wigram, who is working with Inspector Leveret (Donald Sumpter). Leveret had chased them before, but they had managed to escape. Leveret and Wigram take them both to a secluded location where Claire's clothes are found, but her body is still missing. The fateful night arrives. A German U boat locates an Atlantic convoy and begins transmitting. Through the night, the boats transmit 23 messages and Cave is angry that Jericho is still not able to figure out the code. Meanwhile, Hester still has the enigma machine and the 11 messages from ADU. She also works through the night to work out the code.

The U boats start the attack on the second night and ships start going down. By 3rd morning, 4 hits and 300 men lost. Hester figures that her code is a list of Polish names (the ADU unit was digging out Polish Hebrews from mass graves and documenting their names. The Poles were killed by the retreating Russian army). This is why the messages were removed and the receiving station asked to stop recording traffic from ADU. This was too big a secret and they didn't want to embarrass their ally, the Soviets.

In the list Jericho finds a name Adam Pukowski and now knows that Jozef 'Puck' Pukowski was looking for his brother's name in the list. Jericho knows that Jozef killed Claire. Jericho tracks Jozef onto a train to London and manages to get on. He finds Wigram and Leveret already there. Wigram tells Jericho that Jozef and Claire were having sex, and Claire helped him read signal traffic from ADU to look for signs of his brother's name. The Brits wants to keep this a secret as Stalin was helping them win a war.

Jozef wanted to help the Germans (as he wanted to take revenge against the Soviets) and told them about the cracked enigma cipher (which is why they changed the codes). Jozef killed Claire after he came to know that Jericho was coming back as he knew Claire would reveal everything to him. Jericho works out that Claire was Wigram's agent on the park and she told him everything. Jozef escapes the train.

Jericho looks at the Cave's map and finds a U boat being tracked close to Brit shores. He figures that Germans have sent a U Boat to pick up Jozef. He had a postcard from Claire, with the picture of a Scottish village. Jericho tracks down Jozef at the Scottish village, preparing to ride out in a boat to meet the U boat and attacks him (without knowing that Wigram was already tracking Jozef). Jozef wanted to reveal to the Germans about the computer and how the Brits were cracking the Enigma code.

Wigram orders the attack and sinks the U boat and Jozef goes down with it. Jericho meets Wigram and tells him that Claire was not dead. She was hiding and Jozef made contact with her in London to take her with him to Germany. But Claire was not a traitor and she refused. She is still alive, and Jericho is proven right when he sees her crossing a street in London in 1946. Jericho is now married to Hester and expecting a baby.