Episode 5 of "When the Phone Rings" delves deeper into the intricate web of secrets and emotions, picking up moments after the previous cliffhanger. Sa-eon arrives at the festive gathering, Hee-joo's secret still weighing heavily on his mind. His eyes catch Yeon-hui escorting his wife to the lavatory, and he inadvertently eavesdrops on their hushed conversation. Stirred by what he hears, Sa-eon confronts Yeon-hui, inquiring about Hee-joo's continued struggle with selective mutism and warning him to treat her with the utmost respect.
Amidst the lively party, Sa-eon's gaze repeatedly drifts towards his wife, while his father-in-law prods him about joining his father's political campaign. The clock strikes ten, and Sa-eon receives the anticipated call from room 406, prompting him to rush to the rooftop to deliver Hee-joo her jacket. There, he discovers her engaged in a phone conversation, her fear causing her to hide the phone hastily and stumble. In an instinctive rush to steady her, Sa-eon voices his deep concern, fearing she might be contemplating harming herself. Hee-joo, flustered and hiccupping, defies Sa-eon's command to make a sound, frustrating him further as she continues to shield her secrets.
A call from Do-jae interrupts the tense moment, informing Sa-eon that 406 is indeed present within the building. Meanwhile, Hee-joo takes the elevator down, unaware of the looming danger. Realizing her peril, Sa-eon opts for the stairs in a desperate bid to reach her.
Back at the party, Sa-eon finds Hee-joo and hastily phones Do-je, instructing him to scrutinize the guest list for any suspicious figures. Post-party, as they return home, Sa-eon gently inspects Hee-joo's knees for a scar, triggering a nostalgic flashback. Years ago, Hee-joo narrowly escaped a dog's bite, and Sa-eon heroically saved her. He marvels at her remarkable resilience, enduring the pain without a single scream.
That night, both lie awake, tormented by their unspoken thoughts. Sa-eon ponders confronting Hee-joo but acknowledges his own concealed truths, creating a barrier between them. Exhaustion claims Sa-eon during a crucial work meeting, causing Young-woo to fret that his presentation had bored their boss. Later, Sa-eon eavesdrops on Young-woo's conversation with his wife and, intrigued, asks if their marriage harbors secrets. Young-woo, taken aback, reassures Sa-eon that, unless it pertains to finances, there's nothing to worry about.
Elsewhere, Hee-joo and her team are immersed in joyous celebrations, reveling in the fantastic news of her securing the interpreter's position. In the midst of their excitement, Hee-joo inadvertently taps a heart emoji to Sa-eon, which leaves him utterly flustered and spiraling into a whirlwind of overthinking. He responds with a heartfelt congratulatory message, prompting Hee-joo to offer to treat him to a meal as a token of gratitude. Meanwhile, Sa-eon seeks advice from his colleagues on the perfect gift for someone embarking on a new career. Do-jae suggests a suit, leading Sa-eon to invite Hee-joo to accompany him to a boutique.
To their surprise, I-na coincidentally arrives at the same boutique, though they remain unaware of her presence. Sa-eon carefully selects a suit and a stunning blue dress for Hee-joo. While she gratefully accepts the suit, she firmly declines the dress, insisting it's not her style. Undeterred, he takes her to another store and chooses a different dress, gently urging her to abandon her habit of doubting herself. He offers his unwavering support, ready to assist her whenever needed. Meanwhile, I-na secretly trails behind them, observing their interactions from a discreet distance.
As they stroll together, Do-jae calls Sa-eon with startling news: Caller 406 appears to be a woman.
Across the town, You-ri and Sang-woo venture to the eerie old mansion where Sang-woo reveals a haunting tale of his past. He recounts how a boy from the mansion coerced them into a grim game involving the killing and dissection of a cat. A frightened young Sang-woo fled the scene, but the memory has lingered in his mind ever since. He further unravels that following this incident, several children from their orphanage mysteriously disappeared, and he has been driven to uncover the truth behind these disappearances. He's spent years building his brand to gain a platform large enough to shed light on the case. You-ri, feeling apologetic upon discovering his motivations, confesses that she inadvertently shared Sang-woo's childhood ordeal with Sa-eon.
As they drive back to the city, You-ri receives a message, bringing her joyous news of Hee-joo's new job. Filled with excitement, she eagerly anticipates Hee-joo's future endeavors.
As he watches two sisters walk home, he starts recalling how Hee-joo used to help I-na before she got her hearing aids. At the time, Sa-eon was frustrated watching Hee-joo accept everything being done to her. He wanted her to fight or rebel, at least do something for herself.
As he recalls this, he gets a call from Caller 406. This time, Hee-joo brings up I-na’s return since she just got a message from her sister. She is curious if Sa-eon will change his mind after seeing I-na. Sa-eon insists he won’t, and she asks if it is out of responsibility or sympathy that he is staying with Hee-joo. He is about to confess his real feelings for Hee-joo when a truck nearly hits him. Hee-joo sees him and rushes to get him out of the way.
At that fateful instant, she cries out to him, diving into his path to propel him to safety mere moments before impact. Sa-eon, desperate, pleads with her to utter his name once more, yet she insists that no sound escaped her lips. He urges her to speak her heart's desire, cautioning gently that her hands, now injured, must be handled with care. That same night, Hee-joo receives a chilling call from the genuine kidnapper.
The next day, Hee-joo and the fresh crop of interpreters arrive at work for their inaugural shift. Sa-eon vows to master sign language, eager to foster seamless collaboration with his new colleagues. And indeed, later in the day, Hee-joo personally tutors him in the art of conveying thoughts through gestures. To everyone's astonishment, Sa-eon joins them for the team dinner that evening, further perplexing them when he sanctions an overnight retreat for the weekend ahead.
As the group savors their meal, Do-jae's phone buzzes with an incoming call. He excuses himself and leads Sa-eon outdoors, playing a snippet of the call for him, stripped of its modulating technology. The caller's voice, unmistakably female, stirs suspicion in Sa-eon, who can't help but cast a wary eye towards Hee-joo. He promises to forward another audio file to Do-jae for analysis, hoping to uncover any commonalities.
Revisiting Hee-joo's phone conversation with the kidnapper from the previous night, we learn that the caller threatened her for saving Sa-eon from the impending truck collision. He claimed intimate knowledge of the true Sa-eon and harbored a desire to see him suffer. Moreover, he warned Hee-joo that Sa-eon had become suspicious of her.
After his discussion with Do-jae, Sa-eon succumbs to the influence of alcohol at the team dinner, prompting his peers to escort him home. Hee-joo discovers him still slumbering in his car and gently assists him inside. As they stumble and fall together, Do-jae sends a text to Sa-eon, informing him that the audio file he submitted and the kidnapper's call exhibit similarities. However, Sa-eon remains oblivious to the message. The episode concludes with Hee-joo realizing, somewhat startled, that she has inadvertently kissed Sa-eon in their fall. Yet, she doesn't retreat, merely gazing at him as he sleeps peacefully, the moment charged with unspoken tension.
