女犯人貞慧（金允珍飾）在獄中生下了兒子民宇。這個來之不易的小生命對貞慧的意義重大，然而，監獄畢竟不是養育孩子的地方，等到民宇長到18個月，監獄勢必要為他找到一個收養家庭，這對貞慧來說心酸且無奈。監獄的女官方科長一向對犯人持有偏見，但小民宇的出現另這個慣常冰冷的女人也為之心動，并為孩子操持了周歲紀念。但8個月后，貞慧仍要面對和兒子分離的時刻。

某日，監獄內舉行了合唱團的表演，深受感動的貞慧向獄長提議組織一個合唱團，充實大家的精神生活。獄長同意了貞慧的建議，并承諾若他成功組建合唱團，她可以和兒子共同外出。

然而，對於連兒子聽了她的歌聲都會啼哭不止的五音不全者來說，組建一個合唱團對於貞慧是一個艱巨的考驗。但是爲了可以和兒子呆在一起，貞慧決心一搏。這時，獄友紛紛伸出援手，包括曾為大學教授的文玉（羅文熙飾），做過民歌歌手的花子、每天幻想羅曼蒂克故事的延實、緊鎖心門不肯與外界溝通的由美，此外新來的女官娜英也為合唱團的成立提供了精神物質兩方面的幫助。合唱團因母愛和感動組建，必將綻放出更溫暖的花朵…

Moon Ok (Na Moon-hee) was a musical professor at a university, but is now on death row for committing a crime caused by the abuse of her husband and mother-in-law. In prison she meets a young lady named Jeong-hye (Kim Yun-jin) who killed her husband because of physical abuse. At the time of her arrest, Jeong-hye was pregnant and the baby was eventually born in prison. Now 18 months later, Jeong-hye's baby must be given up for adoption. To spend one day with her baby outside of prison, Jeong-hye forms a prison choir group. Moon Ok becomes the conductor for this choir.

The inmates and prison officers are soon touched by the music produced by this group. "Harmony" provides for a unique human drama set within the world of a female prison.