Episode 13 of "Buried Hearts" kicks off with a bombshell revelation: Yeom Jang-seon has dispatched the DNA test results comparing Dong-ju to Il-do straight to Dong-ju's doorstep. The scene then shifts to Il-do, preparing to step out of his house, while Deok-hui, visibly distressed, poses a haunting hypothetical to him – whether he could terminate Seong-hyeon all over again if given the chance. Il-do responds affirmatively, prompting Deok-hui to spill the beans that Dong-ju is, in fact, Seong-hyeon reincarnated – a truth Il-do is already privy to. Meanwhile, Tae-yun notices his father's departure and tails him to a yard bristling with shipping containers.
A flashback ensues, painting a picture of Il-do and Jang-seon in conversation following the untimely demise of Sun-ho and Gyeong-won. It transpires that Il-do was entrusted with the mission to persuade Gyeong-won, yet she steadfastly refused. Jang-seon expresses satisfaction at Il-do's successful disposal of Gyeong-won. He then floats the idea of Il-do tying the knot with Deok-hui, thereby elevating him to the status of Daesan's eldest son-in-law.
After Il-do's exit, another gentleman takes a seat beside Jang-seon. Their discourse delves into Gyeong-won's murky past as an activist-turned-spy, though the specifics remain shrouded in ambiguity. The conversation also subtly hints at Il-do's paternity over Seong-hyeon.
All of this intriguing information is encapsulated within the recording that Dong-ju retrieves from the enigmatic Dandelion files. He listens intently in his car, heading towards a fateful encounter with Il-do. As predicted, Il-do pulls the trigger on Dong-ju, with Jang-seon observing from a distance. At this critical juncture, Jang-seon decides to inform Il-do of Dong-ju's true identity – but Dong-ju is not yet beyond the realm of survival. Jang-seon subsequently instructs Gu-ho's men to intervene.
Il-do is visibly rattled by this revelation, which Dong-ju affirms with his dying breath. Tae-yun bursts onto the scene, compelling his father to desist. Dong-ju seizes the gun and wields it to deter Gu-ho's men from inflicting further damage. However, the bullet wound takes its toll, and Dong-ju's strength wanes. Tae-yun steps in to lend support, while Il-do remains frozen in shock, grappling with the reality that has just unfolded.
The situation escalates when Kang Seong sends Il-do a text, hinting that Dong-ju might be his son. Driven by this revelation, Tae-yun escorts Dong-ju to a modest hospital, where they are soon joined by Won-bae. While Dong-ju recuperates, Tae-yun shares his unresolved anger, vowing never to forgive his father for his past actions.
Meanwhile, Il-do hastily makes his way to Kang Seong's abode. Seong recounts eavesdropping on Sun-ho and Gyeong-won as they unveiled the truth about Il-do's son. As the trio prepares to depart the hospital, Dong-ju urges Tae-yun to return home.
A memory flashes back, revealing Il-do pleading with Sun-ho for assistance to save his ailing father's factory from closure. Sun-ho, unyielding, also warns Il-do to steer clear of Yeom Jang-seon, a suggestion that falls on deaf ears. Frustrated, Il-do storms out and encounters Deok-hui, with whom he debates Sun-ho's rumored illegitimate offspring, oblivious to how far removed from reality their conversation is.
In the present, Il-do confines himself to his room for days, causing Deok-hui considerable concern. Dong-ju visits him, presenting the DNA test results, to which Il-do responds coldly, asserting he would have still eliminated Seong-hyeon had he known of their kinship. Dong-ju, anticipating an apology, is left disappointed when Il-do wonders where to even start. Dong-ju departs, informing Il-do of Tae-yun's worry, and encounters a puzzled Eun-nam outside, asking her to wait patiently for an explanation.
Elsewhere, at their makeshift detention center, Won-bae realizes Yang-chun has absconded, leaving the injured Administrator behind. Yang-chun arrives at Jang-seon's residence, offering his assistance. Il-do bursts in, confronting Jang-seon about his deceit. Jang-seon, unrepentant, taunts Il-do, who surprisingly declares his alliance with Dong-ju.
Returning home, Deok-hui stumbles upon the DNA test in Il-do's room, sending shockwaves through her. Later, she confides in Guk-hui about a scheme to exile Il-do from Daesan, insisting he is unworthy to be Tae-yun's father.
Shortly after returning from their honeymoon, Chairman Cha and Yeong-su are joined by Seon-u, who also takes up residence in the house. Not much later, Jang-seon drops a bombshell on Chairman Cha by revealing that Dong-ju is, in fact, Il-do's son. He further unveils Dong-ju's theft of the national patriotic fund and mutters something inaudible under his breath.
That very evening, over drinks, Chairman Cha probes Dong-ju about his father, casually mentioning the university professor who happens to be Sister Agnes's father. Dong-ju, unperturbed, hands over the codes to his safes and excuses himself. Subsequently, the chairman dials Jang-seon, who urges him to "seize the moment."
Later, Dong-ju confronts Il-do, informing him that he has disclosed the outdated safety codes to the chairman. In response, Il-do announces his severance of ties with Jang-seon and vows to unveil the entire truth to Chairman Cha, aiming to turn him against Jang-seon. Just then, the chairman's call interrupts, revealing his awareness of the connection between Dong-ju and Il-do. He proposes a trilateral discussion at Dong-ju's place the following night.
The next evening, Il-do arrives at Dong-ju's abode, anticipating the chairman's arrival. They partake in some soju, during which Il-do recounts his relentless self-training to suppress any sense of guilt. The pair ponders what life might be like if they could embrace a normal father-son bond. As the doorbell chimes, Il-do opens it only to be ambushed by Yang-chun, who plunges a knife into him. Dong-ju springs into action, struggling against Yang-chun but gradually losing ground. Recognizing the peril, Il-do干预s, grappling with Yang-chun and tumbling down the stairs together. In a tragic denouement, both plummet to their deaths, bringing Buried Hearts Episode 13 to a heart-wrenching close.
