“Big Mouth” is a gripping South Korean mystery and crime drama that revolves around Park Chang Ho, a struggling lawyer known for his inability to win cases, earning him the nickname “Big Mouth” for his boastful but often unfulfilled claims. His life takes a drastic turn when he becomes entangled in a dangerous conspiracy and is falsely accused of being a notorious criminal mastermind called “Big Mouse.”
Park Chang Ho is suddenly framed for being Big Mouse and sent to prison. While battling the harsh realities of prison life, he must unravel the web of lies surrounding him and prove his innocence.

Go Mi Ho, his determined and resourceful wife, works tirelessly to uncover the truth behind the conspiracy. Her intelligence and courage make her a pivotal force in the fight against powerful adversaries.
The drama exposes a corrupt nexus involving influential figures, including politicians and business moguls. The fight for justice becomes a high-stakes game with life-and-death consequences.
Jerry (played by Kwak Dong Yeon), a fellow prisoner and loyal fan of Big Mouse, becomes a key ally to Park Chang Ho, offering both comic relief and critical support.
As Chang Ho delves deeper into the conspiracy, he adopts the persona of Big Mouse to outwit his enemies. The lines between who he is and who he pretends to be blur, keeping viewers guessing until the very end.