In the gripping third episode of "When the Phone Rings," the intricate web of deception and fear continues to entangle the lives of Baek Sa-eon and his wife, Hee-joo. The episode opens with a flashback to Sa-eon's office, where he abruptly ends a call with the kidnapper, who is later revealed to be Hee-joo. The tension escalates as a bomb explodes at the office, fortunately causing no serious injuries. The CCTV footage unveils an unknown man leaving an explosive disguised as a food delivery, casting a shadow of suspicion over Hee-joo.
Sa-eon, swift in his actions, leaves the hospital to ensure Hee-joo's safety, leading to a tense confrontation at home. He attempts to check a mole on her thigh, suspecting her involvement in the bombing, but Hee-joo reacts with anger and questions his motives. His apology and request for her to stay home for her safety only add to the growing mistrust between them.
The following day, Sa-eon's assistant provides new details about the caller and the explosion, but the investigation yields no solid leads. Meanwhile, Hee-joo is thrown into panic, wondering how the explosive incident occurred when all she had done was make prank calls to irritate Sa-eon. In a moment of clarity, she switches off the kidnapper's phone, vowing to end her charade.
Yu-ri and Sang-woo attend an HBC meeting, where Sang-woo discusses an unrevealed crime story from his time at the Nuri Dream Center orphanage. His chilling anecdote is abruptly ended by an alarm, and he excuses himself for lunch with Hee-joo. Sa-eon, checking Hee-joo's phone, finds a text from Sang-woo and a picture of them together with the Nuri Dream Center sign in the background, piquing his curiosity.
Sa-eon manipulates the situation to ensure that he, Yu-ri, Sang-woo, and Hee-joo have lunch together. His cold demeanor makes things awkward, but Sang-woo remains unfazed. When Yu-ri asks how Sa-eon knows Hee-joo, he fabricates a story about a past business meeting. Sensing Sa-eon's unusual behavior, Hee-joo excuses herself to the restroom. During this time, Sa-eon receives a call from his assistant, reporting the arrest of a suspicious man near the scene of the explosion. As Sa-eon prepares to leave, Hee-joo confronts him, accusing him of suspecting her and Sang-woo of wrongdoing.
Sa-eon deflects, questioning how well she knows Sang-woo and pointing out how little they know about each other's pasts. Before leaving, Sa-eon requests Sang-woo's business card. Afterward, Hee-joo heads to her workplace, where she officially applies for the interpreter position at the presidential office. During a conversation with her superior, she reveals her belief that Sa-eon wishes her dead, referencing his chilling words to the kidnapper: "I'll only believe it when I see a corpse." Unaware that Sa-eon had dismissed the kidnapping threat because he didn't believe it, Hee-joo misinterprets his words as a desire for her death.
Back at home, Sa-eon surprises Hee-joo by lying in her bed and asking her to sleep next to him. Though hesitant, she eventually agrees after he assures her he has no intentions beyond offering comfort. As she falls asleep, Sa-eon quietly leaves, watching her thoughtfully. Hee-joo dreams of her childhood, recalling how her mother forced her to fake muteness after a tragic accident in which the chairman's son died, and his daughter became deaf. Her mother saw an opportunity to use Hee-joo as a tool to manipulate the chairman into providing their family with financial support.
Meanwhile, a member of a group opposing Sa-eon kidnaps Hee-joo's father and contacts her via video call. This man, revealed to be her previous kidnapper, threatens her father's safety if she stops using his phone to threaten Sa-eon. To reinforce his threat, he shows her a handful of bloody human teeth. Distraught, Hee-joo rushes to the hospital, where she finds her father resting. The police revealed that human teeth were found in his hand, which did not belong to him. Her sick father mumbles the same words the kidnapper had used, increasing her unease.
The police escort Hee-joo back home, but during the drive, the car's radio malfunctions. Overwhelmed, Hee-joo begins vomiting, prompting the officers to pull over. She breaks down, lamenting her miserable life: a husband who seems to hate her, a manipulative mother, and constant threats from the kidnapper. Just as despair consumes her, a car and patrol vehicle arrive. Sa-eon steps out, addressing Hee-joo as his wife in front of everyone for the first time. His protective demeanor startles her, leaving her unsure of his true feelings.
This episode of "When the Phone Rings" masterfully weaves together the threads of suspense, deceit, and fear, leaving viewers on the edge of their seats as the characters' lives become increasingly entangled in a dangerous game of cat and mouse. The performances are compelling, and the plot twists keep the audience guessing, making this episode a must-watch in the series.