Episode 6 of "When the Phone Rings" opens with Sa-eon immersed in a haunting dream of his youthful self being subjected to an eerie drone. Awakening with a start, he's startled to discover Hee-joo lying asleep beside him on the cold floor. She too stirs from slumber, and both hastily disengage from each other's proximity. In a rush, Sa-eon bolts to his room to compose himself, struggling vainly to recall the happenings of the preceding night. His gaze falls upon his silent phone, which he promptly plugs into a charger.
At breakfast, a pensive Sa-eon inquiries Hee-joo about the night's events, prompting her to query whether he truly desires an unvarnished truth. Ultimately, she remains tight-lipped, and Sa-eon's thoughts are diverted by a call from Do-jae. During the conversation, Do-jae urges Sa-eon to review his messages. Upon learning that Hee-joo is the mysterious caller 406, Sa-eon is dumbfounded but refrains from disclosing this revelation to Do-jae or confronting his wife directly. He endeavors to resume his routine life amidst Do-jae's persistent updates on the unfolding case.
Later, Sa-eon confesses that this revelation has turned his world upside down, leaving him uncertain about the path forward. For his entire life, he believed he held the reins, blind to Hee-joo's unexpected twist. Alongside Do-jae, he realizes they are both callers, and 406 is unrelated to the bombing or the break-in.
That same day, Sa-eon and Hee-joo resume their sign language lessons. With a heavy heart, Sa-eon requests Hee-joo to teach him the sign for "I forgive your wrongdoings." Though Hee-joo complies, Sa-eon eventually due to the sign's complexity, abruptly terminating their session. As he exits, he accidentally drops his files, and upon retrieving them, he notices Hee-joo had intended to teach him a different phrase.
After the lesson, Hee-joo receives a text from I-na, requesting a meeting.
Elsewhere, Ui-yong dispatches his men to investigate I-na's whereabouts and is greatly relieved to discover that she has returned to the country. In his haste to share this news with Kyu-jin, he finds her unperturbed. She is deeply engrossed in her emotions, revisiting the tragic events that shattered their family two decades ago. Ui-hyong accuses her of hypocrisy, reminding her that both of them had felt a sense of relief after their actions all those years ago. A flashback unfolds, revealing that Ui-hyong and Kyu-jin are the parents of the young master, Sang-woo, whom the protagonist met in the now-deserted mansion. That child had a grim habit of ending the lives of his pets, leaving Ui-hyong and Kyu-jin terrified of him. What dark secret did they harbor about their own flesh and blood?
When the families convene a few days later, Ui-hyong takes II-kyeong by surprise by inquiring about I-na. Meanwhile, Hee-joo and I-na chance upon each other at an aquarium. I-na confesses that she has always known Hee-joo could speak. Having undergone surgery, I-na can now hear and urges Hee-joo to abandon her pretense of muteness. However, Hee-joo feels insulted by I-na's presumption that she can dictate when Hee-joo is ready to open her mouth. Through sign language, Hee-joo delivers a stern rebuke, asserting that it is her sole decision. She further declares that she is weary of I-na meddling in her life. Of course, I-na, unaware of Hee-joo's signed messages, remains in the dark.
After Hee-joo storms away, refusing to watch the little mermaid performance, I-na messages her once more. This time, she unveils her agreement with Sa-eon, disclosing that he had requested her hand in marriage and held her captive.
At home, Sa-eon delves into Hee-joo's bags with urgency, seeking the elusive phone. In retrospect, he acknowledges the numerous hints pointing to Hee-joo being 406, yet he overlooked them all. Despite this realization, the nature of her intentions remains a mystery to him. When Hee-joo catches him rummaging through her drawer, her eyes widen in astonishment. He quickly fabricates a story, claiming to search for his own phone. To his dismay, Hee-joo's suspicion deepens as his phone rings from another room, prompting her to gesture towards its location.
Undeterred, Sa-eon persists in his exploration and discovers lingerie nestled within the drawer. His playful teasing ignites a spark, and Hee-joo lunges to reclaim the bra from his grasp. Their light-hearted banter soon gives way to a more intense exchange, culminating in their tumbling onto the bed. Amidst the laughter and flirtation, a flashback envelops Sa-eon's mind, revisiting the tender, albeit accidental, brush of lips from the previous night—a moment too fleeting to classify as their inaugural kiss, yet potent enough to stir his heart. Tentatively, he attempts to broach the subject, but his confusion and embarrassment propel him to flee the room abruptly.
He finds solace in a solitary run, the rhythm of his footsteps matching the turmoil in his chest. At the stroke of 10 pm, 406's call pierces the night, and they agree to a game of truth, posing one question to each other and pledging honesty in return. Hee-joo inquiries about the agreement with I-na, and Sa-eon confesses that Hee-joo alone brought him tranquility, a beacon amid the recurring nightmares that have haunted him since childhood. He admits his proposal was a bid to liberate her, only realizing later that he had inadvertently forged another chain, binding her in a different kind of captivity. He solemnly promises a genuine marriage if that is her desire.
In turn, Sa-eon asks Hee-joo if she seeks a divorce, and her response is a weary sigh, layered with失望. She recounts the three years marked by rejection and distance, expressing her exhaustion from waiting for their circumstances to mend. As they converse, the veil of misunderstanding lifts, and they begin to see each other with clarity, their hearts slowly aligning.
Sa-eon inquiries whether Hee-joo is under some form of duress, and Hee-joo confides that she is, indeed, partially threatened. As their conversation winds down, Sa-eon pleads for the opportunity to provide Hee-joo with the affection she desperately needs. Overwhelmed by the sincerity in his voice, Hee-joo replies ambiguously, hanging up and hinting that it all hinges on Sa-eon's future actions.
The following day, Sa-eon and his colleagues embark on a team retreat. His jealousy flares up when a new recruit lavishes undue attention on Hee-joo. Determined to keep her all to himself, he goes out of his way to arrange adorable, romantic lunches for the entire team. During the group games, he strategically ensures that he pairs up with Hee-joo. After their victorious streak, he promptly asks Young-woo to snap a picture of them, capturing a fleeting moment of camaraderie tinged with something more.
Elsewhere, Sang-woo and You-ri visit the orphanage, where the children eagerly greet You-ri, clamoring for her autographs. Mistaking her for Sang-woo's girlfriend, they eagerly share embarrassing childhood photos of him. While perusing the album, an old photograph slips out, sparking Sang-woo's recognition—it's from his younger days at the orphanage. They seek clarification from the sister in charge, but she admits she arrived after the mysterious disappearance of the children and knows little about it. However, she reveals a startling detail: four children went missing, not three, hinting that one of the twin boys in the picture was also lost.
You-ri is saddened by the fact that no one seems to remember or is actively searching for the missing kids. Sang-woo reassures her, his eyes resolute, that he has not forgotten and that he is, indeed, looking for them.
The narrative transitions to the kidnapper receiving an urgent update, signaling that the status quo has dramatically shifted, heralding the pivotal D-day. As Sang-woo and You-ri make their way back to the bustling city, they devise a meticulous strategy to uncover vital information regarding the whereabouts of the abducted children. Sang-woo vows to reach out to the other twin, hoping he might hold the key to unraveling the mystery surrounding his missing sibling.
Meanwhile, back at the tranquil retreat, the group embarks on a hiking expedition, with Sa-eon and Hee-joo assuming the role of trailblazers. The remainder of the team ambles behind, ascending the mountain at a leisurely pace. En route, Sa-eon thoughtfully offers Hee-joo his jacket, anticipating the chill that might descend later in the day.
Curiosity begins to stir among the team members about the budding connection between Sa-eon and Hee-joo, prompting Young-woo to step in and champion his superior's cause. Upon reaching the summit, the group decides to commemorate their achievement with a group photograph. However, their celebration is abruptly interrupted when fellow hikers recognize Sa-eon and thrust themselves forward for a photo opportunity. In the ensuing tumult, Hee-joo loses her footing and plummets off the platform.
Sa-eon, driven by sheer panic, races down the mountain in a desperate bid to locate Hee-joo, beating the rescue teams to the punch. He returns, breathless and disheartened, reporting that he glimpsed a shattered tree but could not trace Hee-joo's whereabouts. In a bid to aid the search dogs, he hands over his second jacket, hoping its scent will lead them to her.
As dusk descends, anxiety grips the rescuers and Sa-eon, their hopes beginning to falter. News of Hee-joo's plight spreads like wildfire through the media, prompting reporters to flood Sa-eon with calls. He steadfastly declines their pleas for comment, entrusting Do-jae to manage the media circus.
Regaining consciousness, Hee-joo fumbles with her phone, realizing it had sustained damage during her fall. Injured and barely able to move, she attempts to summon help using a black phone, but her calls fail to connect. A haunting memory resurfaces—the kidnapper's warning that the phone was solely programmed to reach Sa-eon.
For a considerable period, she found herself in a dilemma, torn between calling him or not. Ultimately, she made up her mind to reach out, and Sa-eon, endeavoring to conceal his awareness of her true identity as 406, pretended to believe Hee-joo was still in the kidnapper's custody. During their phone conversation, he instructed her to utilize the first-aid kit and flare that he had discreetly placed in her bag. Struggling to unzip her bag, Hee-joo managed to access the flare and activate it. The moment Sa-eon caught sight of the flare, he expressed his gratitude to 406 and vowed to rush to Hee-joo's side without delay. Hee-joo, desperate for his prompt arrival, pleaded with him intently.
In the epilogue, we are enlightened about a pivotal moment from the past. On the evening when Sa-eon was intoxicated, Hee-joo的勇气地探究起他内心的真实情感。 His heartfelt confession of his liking for her left her deeply touched.
