このドラマは、航海中の自動車運搬船「アンピトリテ号」を舞台に、駆け出しの三等航海士として働く坂本真鈴（飯豊まりえ）と、同じく駆け出しの三等機関士として働く石川燕（武田玲奈）が、厳しい上司との対立や、理不尽な異動、悪天候や海賊船との遭遇などのあらゆるトラブルにキュート＆コミカルに立ち向かいながら、一人前の船乗りを目指していく“海のお仕事コメディ”だ。
男性キャストに関しては、一等航海士としてアンピトリテ号に乗り、真鈴ら後輩航海士達に厳しく接して指導する「鬼のチョッサー（=一等航海士）」神崎拓也（かんざきたくや）役に平岡祐太が決定、新人機関士で、真鈴のことを「坂本先輩」と慕いながら密かに恋心を寄せる奥手な犬系メガネ男子の後輩?如月光（きさらぎひかる）役に宮崎秋人、さらに、真鈴とは年の近いムードメーカーの先輩で「筋肉が俺のコスチューム」と公言する筋トレ狂の二等航海士?晴海修作（はるみしゅうさく）役には、この度主題歌の「炎?天下奪取」を歌うBOYS AND MENの水野勝が決定している。
Haunted by the memory of Walter Holderlin, a soldier he killed during World War I, French musician Paul Renard (Phillips Holmes) confesses to a priest (Frank Sheridan), who grants him absolution. Using the address on a letter he found on the dead man's body, Paul then travels to Germany to find his family.
As anti-French sentiment continues to permeate Germany, Dr. Holderlin (Lionel Barrymore) initially refuses to welcome Paul into his home, but changes his mind when his son's fiancée Elsa identifies him as the man who has been leaving flowers on Walter's grave. Rather than reveal the real connection between them, Paul tells the Holderlin family he was a friend of their son, who attended the same musical conservatory he did.
Although the hostile townspeople and local gossips disapprove, the Holderlins befriend Paul, who finds himself falling in love with Elsa (Nancy Carroll). When she shows Paul her former fiancé's bedroom, he becomes distraught and tells her the truth. She convinces him not to confess to Walter's parents, who have embraced him as their second son, and Paul agrees to forego easing his conscience and stays with his adopted family. Dr. Holderlin presents Walter's violin to Paul, who plays it while Elsa accompanies him on the piano.
The film's original title, The Man I Killed, was changed to The Fifth Commandment to avoid giving "wrong impressions in the minds of the public about the character of the story." It ultimately was released as Broken Lullaby.
