昭和16年，小野寺百合子随同身为陆军武官的丈夫小野信前往瑞典的斯德哥尔摩赴任。从抵达之日起，百合子便配合丈夫进行谍报工作，心照不宣。极度危险的境地以及前所未有的压力，让百合子几乎透不过气来，而夫妻俩的行动又无时无刻不在威胁子女们的安全。这一天，一则重要情报传递到百合子手中。根据雅尔塔会议的密约，苏联将正式对日宣战。不知为何，这条情报未能及时传回国内，从而阻断了日本走向和平的道路，不久后原子弹投向日本土地。战后，百合子成为儿童文学翻译，而丈夫却胸怀遗憾，无精打采。在小野寺夫妇的心底，始终有一个不曾解开的谜团，他们决定寻找那封密电的下落……

本片根据小野寺夫妇的真实事迹改编。

Onodera Yuriko sets off for Sweden where her husband, Major General Onodera Makoto, is stationed as a military attache in Stockholm during World War II. Called the "god of intelligence", Makoto is an intelligence officer of the Russian service of the Japanese Army General Staff. Fluent in Russian and German and trusted by the spies of many countries because of his integrity, his office would eventually become the most important Japanese intelligence post in Europe. From the day of her arrival in Stockholm, Yuriko helps her husband's intelligence activities. She encrypts the highly classified information obtained by Makoto and sends it in coded telegrams to the General Staff Headquarters in Japan every day. Husband and wife have jointly undertaken this intelligence work for confidentiality.