The parents of the family were Martín Fierro (no relation with the gaucho literary character) and Lucía Fierro. They had four sons: the young adults Juan and Ezequiel, and the teenagers Lucho and Sandi. Juan is blind, but managed to become a high school history teacher. Ezequiel, an adopted son, works at the butcher shop with Martín and Amadeo, Sandi's best friend. Sandi began to study medicine, but became a vedette instead. Lucho goes to school, and, even through he doesn't know it, is an adopted son as well. And there's even more people at the Fierro house: Lucía's mother and sister Mimicha and Sissi, and Martín's brother Ángel.
Love relations: Juan is torn between his assistant Rita and his student Morena Fontana (daughter of the school's principal). Lucho likes Morena, but to no avail; he would end with Karina, another student. José María Fontana, the principal, is an old love of Lucía, but never saw any action.Despite not knowing it, both Sandi and Amadeo love each other, although he's married to Sandi's friend Mabel and has a son. Don Martín, Martín's father, is gay and lives with his boyfriend Rafa.
It began as a comedy, but by the middle of the year, the series became Darker and Edgier. Martín and Lucía broke up and got new couples, Juan Cruz and Isabel, and Juan's relation with Morena was exposed, leading to his removal from school. He ended married with Rita (who secretly outed his relation with Morena), but Juan eventually left her, and returned with Morena. After several failures to keep him with her, Rita is revealed to be a mad serial killer, and even killed him by accident, when trying to kill Morena. Morena was pregnant, and had a son of Juan after his death.
The series was remade in Mexico as "Alma de Hierro".
Son de Fierro contains examples of:
- A-Cup Angst: Karina suffered this when comparing herself to Morena or her other friends. Behind her back, other students called her "físico de nadadora" (which literally means "swimmer's body).
- Altar the Speed: Rita killed Juan by accident, when she tried to kill Morena in the hospital. The Fierro rushed a wedding, so Juan and Morena could get married. Juan died immediately after the kiss.
- Ax-Crazy: Rita.
- Berserk Button: For Fierro, it's Fontana. For Fontana, it's Fierro.
- Continuity Nod: Martín Fierro is not based on the gaucho by José Hernández, neither it is a parody or homage: he just uses his name. Still, when Fontana takes the bus and they introduce a new character to dispute the love of Lucy... do they had to call him "Cruz"?
- Darker and Edgier: It all began as a comedy, but by the half of the year it became a dark drama.
- Disabled Love Interest: A male one, the blind Juan. More than that, even being blind he was the disputed part of a Love Triangle.
- Dysfunctional Family: To the max! Let's count: Martín, Lucía, Juan, Sandi, Lucho, Ezequiel, Mimicha, Angel, Sissi... 9 people living at the same house! And consider we do not count Amadeo, Morena, Rita, Karina, etc; who do not live there, but spend a lot of time in it.
- Evil All Along: Rita.
- I Am Not Your Father: Lucho is not really the son of Martín and Lucía. Their son had died on birth, and the same day a woman died after giving birth, so she gave her son to them before her demise, and that's Lucho.
- Love Makes You Crazy: Rita was a nice girl at the begining, Juan simply was moe interested in Morena. But Rita moved on and on, doing thing more and more evil and cruel, and in the end she was completely nuts.
- Named After Somebody Famous: "Martín Fierro", the name of the main character, is the same name than the gaucho from the "Martín Fierro" poem by José Hernández, one of the most famous pieces of Argentine literature. It is not an adaption, or even an homage, to the character; he just uses his name.
- Hot Teacher: Juan.
- Magic Plastic Surgery: The new actress playing Sisi
- Put on a Bus: Mario Pasik (who played Jose María Fontana) left the series, to work at El Hombre Que Volvio De La Muerte. His character, the school's principal, left to Spain, and left Lucía in charge of Morena.
- Karina was sent away on a bus too, halfway through the series.
- About twenty or so episodes before the series end, Sandi too, when she's send abroad with her baby.
- Self-Made Orphan: Sort of. Rita killed her stepfather, pinning the murder on her birth mother, who was sent away to an assylum and she was left with no relatives...
- Teacher/Student Romance: Juan and Morena. And it worked... sort of.
- The Bus Came Back: Camila Bordonaba (who played Karina) had legal problems with her contract. Karina was literally Put on a Bus to the very far and distant city of Choele-Choel. But she returned some months later, when the legal problems were solved.
- Throwing Off the Disability: Averted. During a week, Juan went through a delicate operation that may restore his vision... and it failed. He regained his vision when he kissed Morena for the first time, but it was for just a moment. He finally recovered his full vision when he got married with Morena... but considering that he died immediately after the wedding (which was rushed because of his mortal wound), that just makes things more tragic.
- Yandere: Rita. Oh, so much...