Bomi is 12 years old. She wants her own room so badly. Her sister, Eonju, whom she shares the room with keeps sneaking a look at her diary. She studied really hard to get first place as her mom promised to get her own room if she did but her mom keeps denying the promise. So Bomi decides to marry her sister off! She finds out that the manager of a construction company like her sister and does her best to help him. The manager ends up winning her heart and proposes to Eonju. But she refuses his proposal. Bomi gets curious and tries to find out why she doesn't want to get married.
Based on the real life story of legendary cryptanalyst Alan Turing, the film portrays the nail-biting race against time by Turing and his brilliant team of code-breakers at Britain's top-secret Government Code and Cypher School at Bletchley Park, during the darkest days of World War II.