Patricia, a cryptanalyst, introduces Alan Turing to the Engima machine and explains how it works. Alan is tasked with breaking the Enigma machine so that the Allies could read the intercepted German messages during World War II.
After breaking the enigma, Alan Turing and his team discover that there will be an attack on a British passenger convoy, and hundreds of civilian lives are at risk. Hugh starts calling Commander Denniston's office to let him know of the attack, but Turing stops him. Turing's rationale is that it will alert the Germans that they've broken the enigma. Their biggest challenge now is keeping secret the fact that they broke the enigma.
Alan Turing comes to the realization that they can more easily break the enigma code by using produced words that they know will be in every message. The group determines that weather reports are a source of predictable words.