It is based on the novel Die schwarzen Brüder ("The Black Brothers"), written in 1941 in Switzerland by author Lisa Tetzner.

On his journey to Milan, Romeo befriends Alfredo, a kind but secretive boy, and other children in similar circumstances.

Romeo forms a resistance group called the Black Brothers to stand up against a street gang, the Wolf Pack, led by Giovanni.

Meanwhile, Angeletta is revealed to be the granddaughter of Lady Isabella Montgomery, a noblewoman who initially rejects her but later takes her to Paris for medical treatment.

Alfredo is revealed to be from the noble Martini family and was framed for his parents’ deaths by his uncle, Mauricio, who now seeks royal favor.

When Alfredo’s younger sister, Bianca, escapes captivity, the Black Brothers help reunite the siblings.

[1] In interviews in the 90s and early 2000s, the director, script writer, and voice actors acknowledged the common interpretation that Romeo and Alfredo are more than just friends multiple times without confirming or denying it.

[2][1] Later, in a special interview with the director, Kouzo Kusuba, from the 2010 Word Masterpiece Theater Series Memorial Book: Europe Edition, he confirmed that the relationship between Romeo and Alfredo was intended to be romantic.

[5] In 2022, the series received a stage musical adaptation in Japan which was performed at Ikebukuro's Brilla HALL from March 30 to April 3.