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__APOS__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__APOS__s fiancée Elsa identifies him as the man who has been leaving flowers on Walter__APOS__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__APOS__s bedroom, he becomes distraught and tells her the truth. She convinces him not to confess to Walter__APOS__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__APOS__s violin to Paul, who plays it while Elsa accompanies him on the piano.
The film__APOS__s original title, The Man I Killed, was changed to The Fifth Commandment to avoid giving __QUOTE__wrong impressions in the minds of the public about the character of the story.__QUOTE__ It ultimately was released as Broken Lullaby.
