Both were compelling protagonists, but a good story needs villains as well as heroes, and Crash Course in Romance had plenty of them.

Some, like Chi-yeol’s loyal assistant Ji Dong-hee (Shin Jae-ha), who was finally revealed as the story’s hoodie-wearing and catapult-wielding serial killer, are of the variety that populate our nightmares (or our late-night entertainment) but which few of us will encounter in our lives.

Yet most of the show’s villains are types we recognise around us: overzealous mothers trying to get their children ahead at the expense of others, or family members who renege on their responsibilities, like Haeng-ja (Bae Hae-sun), who abandoned her daughter Hae-yi (Roh Yoon-seo) to her younger sister Haeng-seon’s care, only to roll up with a suitcase and an unctuous smile when she sniffs a potential payday.

In Hae-yi’s orbit, another villain is her classmate Bang Su-a (Kang Na-eon). Driven by her mother, Jo Su-hui (Kim Sun-young), queen among the tiger mums, Su-a was the top student in their class. She was flummoxed when Hae-yi, the daughter of a humble neighbourhood business owner, began going toe to toe with her scholastically.

Su-a is cruel to Hae-yi and conspires to keep her down, but she’s also driven by stress and expectations that become so overwhelming, they eventually transform her into a sympathetic character.

One of the most quietly heartbreaking moments in the series comes after she collapses upon learning that she came second to Hae-yi during the all-important mock exams.

After she is discharged from hospital, Su-hui offers her the rest of the day off, only to immediately retract the offer and push her to work even harder to make up for lost time.

The added strain pushes Su-a over the edge and she begins having hallucinations as maths equations rise from the page and swim before her eyes. Her rage towards Hae-yi increases, and she begins having waking dreams of killing her, although thankfully she never goes beyond the point of no return.

Perhaps the greatest villain in the show is society at large, the cause of all the pressures that drive the characters to do bad things.

After the misunderstanding that started their relationship, a misunderstanding that prompted Chi-yeol to break the phone of Haeng-seon’s brother Nam Jae-woo (Oh Eui-sik), Haeng-seon and Chi-yeol eventually formed an uneasy alliance – she provides him with daily lunchboxes, since he can’t keep down other food, and he gives Hae-yi secret classes after she is unfairly expelled from his exclusive “all care programme”.

Their arrangement can’t stay secret forever, and once it does come out, it leads to several misunderstandings. Public scrutiny being what it is, the arrangement has to end, but the problem is that Chi-yeol has already developed feelings for Haeng-seon, try as he might to suppress them.

Haeng-seon is dragged over the coals for providing sexual favours to Chi-yeol to let her daughter get ahead, even though nothing of the sort happened. This falsehood is maintained so that Chi-yeol can avoid taking the blame and damaging his public image.

Then Haeng-seon accidentally attends an education talk without checking who the speaker is. Chi-yeol takes questions from the audience and is grilled over the scandal, but once Haeng-seon is criticised he loses it, owns up and comes to her defence.

“I had a crush on her,” he confesses as he stares at her across the room in the show’s most heart-swelling moment. He saves her but destroys himself, as this makes him the man trying to go after a married woman.

Of course, Haeng-seon isn’t actually married – that’s Hae-yi’s real mother, Haeng-ja.

The violence of the serial killer plot jarred occasionally, particularly the recurring instances of stray cats being killed (thankfully not on screen), but Crash Course in Romance has otherwise been a broadly appealing K-drama series with something for everyone.

Crash Course in Romance is streaming on Netflix.