After his ex-wife moves to Rome, Merlí finds himself solo-parenting and working as a substitute philosophy teacher at his son Bruno’s school, where his unorthodox style intrigues the students, butts heads with faculty, and embarrasses his son.
Merlí encourages his class to participate in the literary contest by cheating, uses Plato to help Ivan, a student with agoraphobia, and takes an interest in the mother of another. Meanwhile, Bruno reveals a personal secret to his friend Tania.
After Merlí gives Gerard girl advice, his interest in Gerard’s mother, Gina, grows when he sees that she’s a fellow straight-talker. He also has a breakthrough with Ivan and steals a test copy that ends up in Bruno’s hands.
After Bruno invites Pol over to study, he lets his feelings slip and complicates their friendship. When they get perfect test scores, they’re accused of cheating and Merlí is also suspected in the scheme. Will it cost him his job?
In the spirit of Socrates, Merlí tells his students they must question the values imposed on them by their parents, which angers Joan’s strict father. He takes Ivan outside his comfort zone to disastrous consequences and gets closer to Gina.
Berta’s home life is revealed, which explains her need for sympathy and attention. Merlí and Gina have a bad fight after she finds out about his relationship with Laia. Merlí keeps pushing Ivan to step out and suggests a visit from Bruno.
Bruno’s fraught relationship with Pol causes resentment towards his father but the two end up having a warm heart-to-heart for the first time. When Pol loses a loved one, Bruno reaches out and breathes hope into their friendship.
After a student catches Merlí and Gina kissing, she wants to keep it from Gerard but he’s turned off by the secrecy. A viral video of Monica inspires Gerard to take a brave stand in support of her. Ivan makes a breakthrough.
The students throw Pol a birthday party, which leads to many revelations. Bruno and Pol grow closer than ever, Gerard learns about his mother and Merlí, and Joan ends up in the hospital after drinking too much. Merlí confesses his feelings for Gina.
Merlí tells Joan’s parents about the alcohol incident, which infuriates Joan but ultimately drives him out of his home and to Merlí. Feeling hopeful, Bruno approaches Pol but is rejected and takes his anger out on the Spanish teacher.
Merlí helps Berta and Pol find direction, encouraging the latter to work with Ivan. Bruno continues to make fun of Santi the Spanish teacher until he gets kicked out of class. A new student arrives who defies expectations.
Merlí encourages the students to boycott the school’s food collection campaign to protest corruption, prompting the principal to take it up with the review board. After Merlí confronts Bruno about bullying Santi, he receives news of a tragic death.
The unexpected death devastates the students, especially Bruno. To help them pay respects, Merlí breaks the rules once again and is on the verge of losing his job. His students make a grand gesture of support. Ivan is ready to return to class.
