Episode 11 of "Undercover High School" kicks off with Hae-seong delivering a bombshell to Seok-ho: the vault contains no gold bars. Hardly has the revelation settled when Seo Myeong-ju bursts in with her entourage, compelling Seok-ho to grant her access. Myeong-ju's desperation spirals into hysteria as she futilely searches for the nonexistent treasure.
With a heavy heart, Hae-seong retreats to his abode, carrying his father's suit and watch as mementos. Amidst the relics, he discovers a bullet, a grim reminder of past conflicts. Meanwhile, Jeong Jae-hyeon's funeral gathers Hae-seong's fellow students under a somber sky, united in their mourning.
Seok-ho imparts to Hae-seong that the bullet is from a Glock 17, a weapon once issued to NIS agents, recalling Director Kim's report of a missing round from days gone by. Myeong-ju's frustration over the vanished gold reaches a crescendo when Principal Park informs her that the room, upon investigation, turns out to be a conference space for Seo Byeong-mun, far from a vault.
On Director Kim's orders, Hae-seong receives a chilling text: his employment has been terminated. Returning to his home, he retrieves a firearm, a resolve hardening within him. As he prepares to depart, Soo-a intercepts him, urging him to join their gathering at the restaurant. With a gentle but firm refusal, Hae-seong bids her farewell, entrusting her with his thanks and proceeding on his solitary path.
Soo-a relates Hae-seong's enigmatic parting words to Seok-ho and the group, their collective realization dawning that he is on a mission to confront Director Kim. Kim, currently ensconced in a hotel for a conference, becomes Hae-seong's target. Armed and determined, Hae-seong locates Kim's room number and storms in, gun aimed at Kim's temple. A struggle ensues, with Kim managing to alert the reception during the fray. Kim's secretary, sensing the gravity of the situation, swiftly summons security.
The secretary and his entourage burst unannounced into Kim’s room, cutting off any chance for Kim to utter a word. As if on cue, the security personnel whisked Hae-seong away, precisely as Seok-ho and their companions stepped into the fray. A daring plan unfolded: NIS agents would engage the secretary and his men in a diversion, while Soo-a, armed with a fire extinguisher, orchestrated Hae-seong’s rescue and their subsequent escape.
Meanwhile, at the school's administrative core, Seo Myeong-ju implemented a harsh decision—slashing scholarships and hiking tuition fees by a staggering 50%, all in the name of securing much-needed funds. Principal Park harbored doubts about this drastic measure, yet he was merely instructed to uncover the hidden gold, leaving him with little choice.
Back at their hideout, Hae-seong could scarcely believe that his team and Soo-a had genuinely believed he was poised to take Director Kim down. He disclosed that the ominous threats were merely a smokescreen. In truth, Hae-seong had seized the moment to infiltrate Kim’s phone, setting up surveillance to keep tabs on him.
At school, the bombshell announcement of the tuition hike sent shockwaves through the student body. Soo-a, incensed, marched straight to Myeong-ju’s office, informing her that 150 students faced eviction due to this exorbitant increase. Myeong-ju mocked her desperation, and after an intense verbal spat, Soo-a left, throwing a parting shot about Myeong-ju's solitude.
Later, Director Kim paid a visit to Myeong-ju at her residence, with Hae-seong eavesdropping on every word. With Kim's bullet now discovered, he sought Hae-seong’s removal, but Myeong-ju was convinced Hae-seong held the key to her missing gold. The ensuing spat saw Kim accusing Myeong-ju of firing the fatal bullet that claimed Jae-hyeon’s life, escalating tensions to a boiling point.
A nostalgic flashback transports us back to the poignant moment when Jae-hyeon bids Hae-seong a final farewell. Outside, Kim looms with a firearm in hand, escorting Jae-hyeon to the school where Seo Myeong-ju interrogates him relentlessly about the gold. Despite Jae-hyeon's insistence that the concealed vault lies empty, Myeong-ju remains unconvinced. In a daring escape, Jae-hyeon narrowly evades capture, only to be shot by Myeong-ju, utilizing Kim's weapon. As he flees her henchmen, Jae-hyeon seeks refuge in the downstairs vault, realizing with horror that he is bleeding profusely. With his final breath, he offers a heartfelt apology to Si-hyun before losing consciousness.
In the present, Myeong-ju coldly refuses to lend Director Kim a helping hand, prompting him to threaten to testify against her before departing. Hae-seong, having overheard everything, phones Kim and proposes an alliance to bring Myeong-ju down. Kim urges a face-to-face meeting, but upon Hae-seong's arrival, he discovers Kim gravely wounded. Suddenly, an unseen assailant renders Hae-seong unconscious as well.
When Hae-seong awakens the next morning, he finds himself next to Kim's lifeless body in the car, a knife clutched in his hand. The police swiftly arrive and take him into custody. Meanwhile, Seok-ho and his team unearth a recording at Hae-seong's residence, wherein Kim accuses Myeong-ju of murder. As the police descend upon the house to conduct a search, Mi-jung attempts to sneak away with a copy of the voice recording but is caught red-handed. The lead detective subsequently forwards the recording to Myeong-ju, who promptly destroys it.
Myeong-ju visits Hae-seong in detention, probing him about her missing gold. When he remains silent, she grants him a single day to reconsider. During his transfer from the police station, Hae-seong engages in a fierce struggle with his guards within the moving vehicle, causing it to plummet off the road and crash. Though severely injured, Hae-seong manages to extricate himself from the wreckage.
From a payphone, he frantically calls Soo-a for assistance, but his voice trails off into silence as he succumbs to unconsciousness, leaving Undercover High School Episode 11 on a cliffhanger, with Hae-seong's whereabouts unknown.
