Episode 4 of "Ms. Incognito" opens with Dong-min making an unexpected appearance at the kindergarten, his ears perking up at the sound of Mi-seon addressing Se-mi as "madam." In a swift attempt to divert his attention, Mi-seon feigns a phone conversation, skillfully steering the topic away. Dong-min, puzzled by his sister's odd behavior, finds himself unceremoniously ushered out by her.
In the seclusion of privacy, Mi-seon acquiesces to Young-ran's proposition, vowing to safeguard her secret from the prying eyes of Muchang's close-knit community. Yet, a wave of unease washes over her upon discovering that both Young-ran and her mother bear the mark of ex-convicts. Young-ran, unfazed by her past, exudes an air of nonchalance, while Mi-seon appears visibly shaken.
Meanwhile, the villagers remain perplexed by the sudden installation of CCTV cameras but choose to overlook them, attributing the change to some unfathomable reason. Seizing the opportunity, Young-ran extracts information from the technicians about the setup and gains remote access to the cameras via her smartphone.
Mi-seon, in an effort to quell Dong-min's growing suspicions, urges him to remain calm. She concocts a tale for her brother, falsely claiming to have conducted a thorough background check on Se-mi. Simultaneously, Seon-young lodges a complaint with the police regarding Young-ran's mysterious disappearance. Initially met with reluctance, the officers agree to register the complaint after receiving a directive from the section chief.
Elsewhere, Dong-hong and his cohorts embark on a quest to locate So-young, Young-ran's mother. Their path intersects with Hyeon-ok, a friend of So-young's, who remains tight-lipped about her whereabouts. Undeterred, Hyeon-ok promptly alerts So-young to the impending danger. Young-ran's confidante, Byul-nae, shadows So-young, uncovering the identities of those in pursuit. She promptly relays this information to Don.
A heated altercation ensues between Don and Hye-ji, the latter's curiosity piqued by Young-ran's abrupt vanishing act. Hye-ji's snooping leads her to the revelation that Don is holed up in a clandestine vault within Chairman Seong-ho's cabin, though the exact location eludes her grasp for the moment.
On the flip side, Young-ran (posing as Se-mi) is struggling to forge a connection with the lively kindergartners. In a misguided attempt to quell their energy, she resorts to showcasing her fighting prowess, only to accidentally rip apart their beloved inflatable dinosaur. The children erupt into tears, sending Young-ran into a panic.
Hearing the commotion, Dong-min abandons his PE class to rush to Se-mi's side. Meanwhile, Mi-seon is distractedly conversing with a salesman and inadvertently places an order for a mountain of toys using the students' fee money. In a private confrontation, Dong-min lambasts Young-ran over her teaching methods, emphasizing that the students have already endured the departures of over five teachers.
Mi-seon returns to her office to discover an empty envelope where the fee money should be. She summons Young-ran to her cabin, demanding to know the whereabouts of the cash. Feeling betrayed by Mi-seon's lack of trust due to her past, Young-ran utilizes the CCTV footage in her room to trace the culprit.
Dong-min, suspecting that Se-mi might flee after resigning, gives chase. Both Se-mi and Dong-min encounter Manager Kim, the man Mi-seon had paid for school supplies. Se-mi swiftly accuses him of theft and drags him to the police station. There, Mi-seon offers her apologies for the misunderstanding, and Se-mi, feeling remorseful, compensates Manager Kim from her own pocket for the false accusation.
On their return journey to the school, Dong-min extends an apology to Se-mi for his harsh words. He advises her that not everything requires a monetary apology. Se-mi retorts that she has the means and chooses to offer it to someone in greater need than a mere verbal apology. She returns to the school, mends the inflatable dinosaur, and eventually makes her way home.
On her way back, a student's mother picks Se-mi up and engages in small talk. The woman subtly tries to pry into Se-mi's culinary preferences. Se-mi (Young-ran), ever vigilant, notices the woman conversing with Jung-hwa, a fellow villager, on the phone and becomes wary. She fibs about her favorite dishes, mentioning those she once spotted in Seong-ho's fridge.
Meanwhile, at the Ga residence, Hye-ji stumbles upon the secret cabin by chance. She is taken aback by the CCTV room, which holds a treasure trove of information about Young-ran's current whereabouts and her guise as Bu Se-mi, the teacher. Outside the house, Butler Choi and Cheol-su encounter Hye-ji and implore her to assist them in locating Young-ran.
Hye-ji is brusque with the two former employees, keeping her discoveries about Young-ran under wraps in a bid to shake them off. Inside the house, she muses to herself, realizing she stands to make more money by sharing the information directly with Seon-young, rather than splitting the proceeds with the duo.
In Muchang, Ju-won escorts Se-mi to his abode, where a breakfast spread awaits, prepared by Dong-min. Ju-won stumbles upon a message on Dong-min’s phone, revealing that the villagers are gossiping negatively about Se-mi. She consults with Lee Do, who advises that Young-ran should endeavor to cultivate friendships with the villagers.
Dong-min and Tae-min arrive at Se-mi’s doorstep, bearing strawberries and liquor, but she declines both offerings. The following morning, Se-mi adorns herself with makeup and announces to Lee-joon’s mother that she intends to host a gathering for the villagers at her residence. She also enlists Mi-seon’s assistance in purchasing the necessary provisions for the soiree.
Mi-seon, with Dong-min’s aid, gathers the groceries, though he is taken aback upon spotting Se-mi alongside Sung-tae. Mi-seon urges her to exhibit a bit more trust. Meanwhile, at the Ga residence, Don is alarmed to discover Hye-ji’s absence and the vault in Seong-ho’s room left ajar.
Back in Muchang, Se-mi erects an inflatable children’s tower in a strategic move to win over the youngsters. As she prepares for her party, Dong-min drops by to deliver additional beverages. Fearful that Dong-min might catch sight of the CCTV cameras displayed on her laptop, Se-mi (posing as Young-ran) clutches him and feigns a kiss.
She swiftly closes the laptop and pulls away, only to be interrupted by Hye-ji’s entrance. Hye-ji introduces herself as Se-mi’s confidante and extends her greetings as the episode draws to a close.
