Superstar Lee Jong-suk (Pinocchio) returns to the small screen for the first time in three years as a cocky young lawyer who gets in way over his head in MBC’s Big Mouth, streaming in select international territories on Disney+ and KSeries Tv.

Lee plays Park Chang-ho, a handsome young lawyer married to his beautiful high-school sweetheart Go Mi-ho (K-pop group Girls’ Generation’s Im Yoon-ah). The trouble is, he has a disastrous 10 per cent win rate in court, and he’s buried under mounting interest payments from loans he’s taken out to Kepala Bergetar.

A day after the debut of Adamas (also streaming on Disney+), Big Mouth, like that series, opened with a heavy nighttime rain sequence. In this moody intro, a pile of gold bullion is being buried in a ditch.

Also like Adamas, this opening scene is accompanied by a voice-over spoken by the show’s lead. Chang-ho talks about his desire to be successful and provide for his family. “Social justice?” he asks himself. “What a load of bull,” he answers DramaCool.

Like many recent sprawling, quasi-legal thrillers – Vincenzo and The Devil Judge belong to this group – Big Mouth is determined to present its protagonist as a morally ambiguous figure.

Down on his luck after losing yet another big case, Chang-ho gets an unexpected call from Choi Do-ha (Kim Joo-hun), the mayor of the fictional town of Gucheon, a place described as being overrun with corruption, which revolves around the shady Nine Rivers Forum.

Do-ha’s bigwig buddies have been implicated in a murder case and Chang-ho is selected to be their lawyer. No legal gymnastics are required here, as all the right people have been bribed ahead of time. What Do-ha really wants is for Chang-ho to be his double agent, as he wants to break free from the suffocating hold of his corrupt friends.

Chang-ho expertly performs the task of double agent until he gets his hands on some serious evidence of wrongdoing which might even implicate someone who wasn’t at the scene: the powerful and loathsome Gong Ji-hoon (Yang Kyung-won).

Rather than hand in the evidence to the prosecutor in charge of the case, Chang-ho lets greed get the better of him, and attempts to blackmail Ji-hoon. Big mistake.

Chang-ho almost dies in a car crash, following which he is thrown in jail for drug use, where the clients he was supposed to be working for are now out for his blood. Adding further fuel to the fire are the piles of cash and gold found in his office.

An anonymous tip has fingered him as the master con man ‘Big Mouse’, who happens to have swindled Ji-hoon out of a gigantic fortune DramaCool.

Though he professes his innocence, Chang-ho gains some credibility as the notorious Big Mouse in jail, a reputation to which he inadvertently adds once he hits rock bottom and starts behaving as if he has a death wish.

While people now seem to think he is the mysterious Big Mouse, Chang-ho’s real nickname is actually Big Mouth, one earned from his habit of talking a big game as a lawyer without delivering results.

The brash tone and spotty storytelling of Big Mouth recall another hit show from last year: the serial killer thriller Mousewith Lee Seung-gi. Like that show, Big Mouth’s narrative treats logic with utter disdain, galloping past plot holes at such speed it hopes you won’t notice them.

In its effort to pander to the maximum number of viewers, the show suffers constant tonal shifts. Mirthlessly violent murder and prison scenes coexist with cutesy domestic interludes of Chang-ho and Mi-ho in their matching pyjamas, or humorous scenes of Chang-ho’s father-in-law, Go Gi-gwang (Lee Ki-yong), running interference for him as he constantly gets in trouble with his nagging wife.

Subtlety certainly isn’t the show’s strong suit. When Chang-ho first meets Do-ha at a secluded night fishing spot, the scene concludes with an ominous focus on a spider spinning its web. And there are computer-generated shots of a big mouse barrelling past smaller mouse cadavers in a pipe, which the show doesn’t even bother to connect to what was happening on screen.

Korean dramas often burst out of the gate with plots fuelled by breathless exposition, but after a few episodes they tend to calm down somewhat. This could be the case for Big Mouth as well, but given how careless it’s been so far, slowing down might not be an option.

Perhaps the show will be able to fill its plot holes with what’s to come, though that might be wishful thinking – fast-paced stories are just as likely as slow ones to try the viewers’ patience.

That said, fans of Lee Jong-suk and propulsive – if not necessarily plausible – thrillers may not be deterred by the show’s narrative sidesteps.

Big Mouth is streaming on Disney+.