The story of No Tail to Tell unfolds in the Joseon era, where Eun-ho, a nine-tailed fox, aspires to cultivate virtue through good deeds and transform into a human. Her closest friend achieves human form and prepares for her beloved's wedding. However, on this joyous occasion, Eun-ho witnesses her friend's future—a life riddled with hardships and suffering. This revelation leads Eun-ho to view human existence as fragile, replete with pain and devoid of worth. Consequently, she abandons her desire to become human.
The narrative shifts to the present, where Eun-ho remains unperturbed as a man is tied up and bleeding to death. The actual tale commences nine years prior. Hyeon Woo-seok, a wealthy and skilled high school student, is poised to be recruited by the youth national football team. However, his classmate, Kang Si-yeol, steals the spotlight. Despite the Hyeons' contributions to the school, the coach unjustly punishes Si-yeol for disrupting Woo-seok's prospects. It is revealed that Si-yeol, who lives with his ailing grandmother, pretends to have a scholarship and funds his expenses through part-time food deliveries. No one is aware of this, and Woo-seok is shocked when he discovers the truth.
Eun-ho, now indulging in granting wishes to the rich for an exorbitant fee, sets her sights on CEO Lee Yoon of the corrupt Geumsu Construction. He brutalizes his driver for turning off the radio and attempts to secure a redevelopment project through bribery. Eun-ho steals the money and manipulates the vote in his favor, subsequently taking him as her client. However, she adheres to certain rules: she will only fulfill the wishes she desires and will never perform a good deed or major misdeed, as these could result in her transforming into a human or losing her powers, respectively.
Eun-ho then forces a fashionable girl to accompany her on a shopping spree, venting about the misconceptions surrounding her kind and how she is the sole remaining one. She recounts centuries of using her powers to manipulate people for amusement. When the girl suggests that Eun-ho has never accomplished anything significant, the fox is offended.
Meanwhile, across the street, Woo-seok attempts to buy Si-yeol new shoes. Si-yeol resists being seen as a charity case and tries to leave, but bumps into Eun-ho due to her superhuman strength. Although he is injured, he worries about her instead. She remains arrogant, and he merely apologizes.
As Eun-ho watches him and Woo-seok depart, she glimpses the future. Her gaze alights on one of the boys, and she confidently predicts that he will become exceedingly famous and wealthy. She even contemplates taking him as a client to reap the financial rewards. When a supernatural stranger abruptly labels her a beast, she is rudely dismissed by the girl. However, the stranger, Lord Pagun, carries a warning from Heaven. She has been exploiting loopholes for too long, and her scale is now tipping. Soon, she will have to choose between becoming human or facing annihilation. Eun-ho scoffs at the warning and walks away.
Outside, Woo-seok apologizes to Si-yeol, and they reconcile by playing football. Eun-ho is heading home when Si-yeol kicks the ball too far and inadvertently hits her. Woo-seok heads home, while Si-yeol goes to retrieve the ball. Instead, he encounters an annoyed Eun-ho. They bicker, and as she looks down on him, he asserts that he will one day become famous. She reveals that it is Woo-seok who will achieve fame; it is his future she foresaw. And the future she sees is immutable and unalterable.
At the crossing, a drunk CEO, Lee Yoon, crashes his car into Woo-seok. Si-yeol rushes to save his friend, only for Lee to drive off. Seeking justice, Si-yeol reports the incident to the police and refuses to accept Lee's scapegoat. Annoyed, Lee calls Eun-ho for his next wish. For double her fee, she is tasked with manipulating Si-yeol's memory of the incident.
She visits Woo-seok in his hospital room and sneers at Si-yeol when she recognizes him. As she attempts to alter his memory, she witnesses a different future. His fate has been swapped with Woo-seok's. Si-yeol will become the famous player. She collapses in pain and he catches her, revealing her tail in the process.
