Episode 4 of "Mercy for None" kicks off with an intense encounter between Chairman Bong-san and Yeong-do, the enigmatic sunglasses-clad figure from previous episodes. Bong-san confidently declares that he has resolved the matter concerning Ju-woon and that the only task remaining is to deal with Gi-jun, for which he assigns Yeong-do the grim duty.
At the secure hideout, an unexpected contingent of men storms in, brutalizing Jun-mo's guards with impunity. It transpires that Jun-mo himself orchestrated their arrival. Among them stands Jeong In-seok, a former champion fighter whose illustrious career was marred by his expulsion from the sport. Jun-mo dangles a lucrative offer of one billion won to Jeong and his compatriot, tasking them with eliminating Gi-jun.
Elsewhere, Gi-jun seeks refuge with a physician to tend to his wounds. As he waits, Byung-ho phones to inform him of an impending meeting with Ju-woon, aiming to broker peace through established rules. However, the conversation is abruptly halted as Jun-mo, flanked by his hired muscle, barges into Byung-ho's office. Byung-ho cautions Jun-mo against pursuing Gi-jun, a warning that incenses Jun-mo into a violent rage, striking Byung-ho with a baseball bat. Chun-seok arrives moments too late, his heart wrenched to see Byung-ho lifelessly sprawled on the floor. In a fit of manic fury, Jun-mo uses the same bat to end Chun-seok's life. When Gi-jun calls, Jun-mo gleefully answers, revealing the grim fate of his friends and tauntingly providing the address to the safe house.
Devastated, Gi-jun rushes to Byung-ho's office and beholds his fallen comrade. Grieving, he picks up the newly crafted bat, a gift from Byung-ho, and sets off with a heavy heart.
Meanwhile, Chairman Bong-san orchestrates the abduction of Detective Han, accusing him of foreknowledge about Gi-seok's impending demise and leveraging this suspicion to coerce more information from him. The scene pulsates with tension, painting a vivid picture of Bong-san's ruthless determination and Han's plight.
Meanwhile, Jun-mo summons a sizeable crowd to the safe house, dangling a substantial sum of money as a reward for delivering Gi-jun to him – alive. Shortly thereafter, Gi-jun arrives at the safe house, diving headfirst into the chaos, engaging in fierce combat. Once he brings down one of the bulkier adversaries, many of the others flee in terror.
Jun-mo finds himself in a state of panic, while Jeong In-seok, assured of his own prowess, demands double the agreed-upon payment. In another corner, Detective Han plays a recording for Bong-san, where a voice instructs the detective to frame the runaway kids for Gi-seok's murder. Bong-san's expression betrays recognition of the voice.
Eventually, Gi-jun breaches the room where Jun-mo awaits, initiating a fierce battle with In-seok. In-seok proves to be a formidable foe, pushing Gi-jun to his limits. The tide turns when Gi-jun, wielding a shard of glass, plunges it into In-seok's eye. After a relentless assault, Gi-jun finally prevails.
Desperate, Jun-mo brandishes a gun, but Gi-jun is within striking distance, disarming him with ease. Jun-mo resorts to pleading for his life, screaming that Gi-seok's fate remains sealed regardless. With a swift swing of his bat, Gi-jun ends Jun-mo's life.
Gi-jun subsequently contacts Bong-san, who was about to reveal Jun-mo's innocence in Gi-seok's murder. However, Gi-jun cuts him off, asserting that, according to their unspoken rule, Jun-mo is now deceased.
A fleeting memory resurfaces, with Gi-seok suggesting they meet more frequently. As Gi-jun drives back, another vehicle slams into him, sending him careening off a bridge and plunging into the river below. A man with a tattooed hand emerges from the attacking car, informing someone on the phone that Gi-jun has met his end.
