Episode 4 of The Frog, titled "I Think She Killed a Child," delves deeper into the enigmatic characters and their motivations, revealing shocking secrets and escalating tensions. The episode begins by revisiting the past, where Sang-jun, filled with excitement, shows Eun-gyeong and Gi-ho around the motel before their purchase. A flashback to his wife's suicide note reveals a heartbreaking message for Gi-ho, expressing her love and longing for peace.
In the present day, Yeong-ha's obsession with uncovering the truth about Sung-a's involvement in Si-hyeon's disappearance intensifies. He visits his daughter, Ui-seon, in Seoul, driven by a deep-seated belief that her life is in danger. Meanwhile, Sung-a continues her secretive activities, leaving Yeong-ha on a relentless pursuit.
As Yeong-ha's investigation unfolds, he discovers a trail of clues leading to Sung-a's involvement. He learns that she made the reservation for the motel under Si-hyeon's name and that the phone number provided is out of service. His suspicions deepen as he finds evidence of her presence at the motel during the time of Si-hyeon's disappearance.
However, Yeong-ha's attempts to uncover the truth are met with obstacles. He struggles to access Sung-a's laptop, which holds crucial information. Despite his efforts, he is unable to break into the device without potentially destroying the data.
As the episode progresses, the tension between Yeong-ha and Sung-a reaches a boiling point. Yeong-ha's confrontations with Sung-a escalate, culminating in a shocking act of violence. In a moment of rage, he attacks her, nearly drowning her in the pool.
Sung-a survives the ordeal, but her facade of composure begins to crumble. Her obsession with art becomes increasingly evident, and Yeong-ha's relentless pursuit forces her to confront her dark secrets. Despite her attempts to evade his accusations, the evidence against her mounts.
The episode concludes with a dramatic confrontation between Yeong-ha and Sung-a. Yeong-ha presents his evidence, including the dashcam footage, bloodstains, and missing towels. However, Sung-a remains defiant, dismissing his claims as circumstantial and threatening to expose his own involvement in the cover-up.
The episode ends on a cliffhanger, as Yeong-ha hesitates to turn in the recording of his conversation with Sung-a. His fear of incrimination leads him to reconsider his actions, leaving the audience wondering about his ultimate decision.