"Impossible Heir" begins with Tae-oh at a crime scene, weapon in hand, with no memory of events. Flashback: Tae-oh moves to his mother's hometown and meets In-ha, the illegitimate son of the Kang Oh Group chairman. In-ha bullies Tae-oh, but they eventually become friends. Tae-oh’s stepdad, wrongfully imprisoned, knows Tae-oh's mom is alive and sends thugs after her. Tae-oh joins a boxing club to protect his mom. He and In-ha plan to climb the social ladder. In college, Tae-oh helps In-ha study and tutors his sister. They form a plan against the scheming family, aiming for the Kangho Group's succession. Tae-ho rejects Hye-won's request, and she warns him not to interfere. At home, he finds In-ha eating. At lunch, Hee-ju wants In-ha over for the weekend. The Kang family disrespects In-ha, except Hee-ju. Mr. Kang agrees, angering Geom-seok. Mr. Kang knows about In-ha's inheritance waiver and assigns his assistant to protect it. Hee-ju arranges In-ha's visit, disappointing him. Hye-won, working at a restaurant, hints at interest in Tae-oh. In-ha faces hostility from the Kangs. Tae-oh comforts him. Hee-ju runs away after being slapped by Geom-seok. She confesses to Tae-oh, who rejects her. Hye-won faces loan sharks. Tae-oh advises her to flee, but she refuses. In-ha and Hye-won kiss. Tae-oh, conflicted, sees Hye-won again but chooses In-ha. Five years later, Tae-oh and In-ha work for the successful Co-prosperity Cooperation Centre, still under Mr. Kang's scrutiny. Professor Chae becomes president of the development center and meets the chairman’s council. Tae-oh writes Chairman Joong Mo's speech, and Joong Mo tests him, revealing he knows Tae-oh's real name and past. Joong Mo makes Tae-oh his assistant. Five years later, Joong Mo faints but recovers. His family discusses Tae-oh becoming chief secretary. Joong Mo focuses on the "Royal Road" project. In-ha works in R&D, and Na Hye is in political campaigning. Seong-joo schemes for power, but Tae-oh and In-ha counter. Hye-won records Seong-joo’s plans. Geum-suk learns Joong Mo's heart condition. Joong Mo transfers a center, demotes Seong-joo, but faces embezzlement charges. Joong Mo collapses; Geum-seok ignores his need for medicine. Tae-oh calls an ambulance for Joong-mo, halting the prosecutor’s raid. At the hospital, Joong-mo's family arrives but shows no genuine concern. Tae-oh asks them to leave, and Geum-suk lies about Joong-mo's collapse. In-ha worries about their plan, but Tae-oh reassures him. In-ju offers Tae-oh a job, but Tae-oh declines. Hye-won hints at marrying In-ha. Joong-mo's heart attack is revealed as a ruse, orchestrated by him and Tae-oh. Tae-oh drafts a contract for In-ha. Hee-ju rejects her arranged marriage and proposes to Tae-oh, who refuses. Seung-joo is framed and summoned by prosecutors. In-ha admits setting up Seung-joo, and Joong-mo warns Geum-suk. Tae-oh and In-ha plan their next steps. The chairman admits guilt to the prosecutor, but a pen drive from Tae-oh exposes the legal system, freeing him and making the prosecutor the scapegoat. In-ha joins the Kang-oh group, worrying the older siblings. Tae-oh becomes Division Director, In-ha Chief Manager, and Geum-seok is sent away. Seung-joo is warned to keep a low profile. In-ha is tasked with selling Kang Oh Tech One. He proposes to Hye-won. Tae-oh meets a hacker. Hee-chan tries to date Hee-ju. A negotiation trap leads Daejong to buy Kang Oh Tech One. The chairman expresses concerns about In-ha. Later, Tae-oh is attacked and loses consciousness. Tae-oh is hospitalized after an attack, and Hye-won arrives, worried. Barely conscious, Tae-oh asks Hye-won not to leave. The chairman permits In-ha to marry Hye-won. In-ha stops the investigation to protect Kang Oh. Suspicious, Hye-won questions In-ha, but he dismisses Tae-oh's importance. Hye-won’s mother demands money, and Hye-won threatens self-harm to escape. U-wan discovers In-ju’s secretary attacked Tae-oh. In-ha brings Hye-won to meet his family. Tae-oh vows revenge on In-ju’s secretary. Tae-oh and Hye-won confess their love. In-ju threatens Hye-won with a photo of her and Tae-oh. The scene cuts to Tae-oh waking up covered in blood, near unconscious In-ju. Han Tae-oh investigates In-ju’s drug network for revenge. In-ju uses photos of Tae-oh and Hye-won kissing to blackmail Tae-oh, threatening Hye-won’s safety. At In-ju's club, In-ju forces Tae-oh to kneel and take drugs, causing Tae-oh to hallucinate. Tae-oh wakes up as a murder suspect for In-ju and his mistress’s deaths. The Kang family is shocked. In-ha and Hye-won, returning from their honeymoon, are concerned. Tae-oh, unable to remember due to the drugs, faces accusations. In-ha takes Tae-oh’s job. Tae-oh, recalling fragments of the night, collaborates with Uwan, posing as his lawyer, to uncover the truth. In-ha confronts Tae-oh and Hye-won about their relationship. Tae-oh recalls details of the night In-ju drugged him and suspects the driver. Joong Mo learns Gi-jun is linked to In-ha. Uwan tracks Gi-jun and discovers his close ties with In-ha. Tae-oh is sentenced to death, shocking the Kang family. In-ha desires Tae-oh's death despite potential sentence reduction. In-ha violently confronts Hye-won. Hye-won visits Tae-oh for advice on joining the Kang Oh art foundation. Tae-oh arranges a phone to find the driver. Uwan discovers Roy's loyalty to Gi-jun. Hye-won is appointed director of the art foundation. In-ha plans to kill Tae-oh. In-ha learns Uwan’s background as a former North Korean intelligence agent. Uwan's assistant betrays him for In-ha. Tae-oh escapes from prison, worrying Hye-won. Gi-jun apologizes to a prison guard for failing to kill Tae-oh. Uwan overpowers his assistant and switches sides for money. The chairman helps Tae-oh escape, revealing In-ha's assassination plot. Hye-won is trapped by Gi-jun and sedated. In-ha confines her to a psychiatric hospital. Tae-oh collaborates with the chairman to thwart In-ha and regain his position. The chairman proposes a company split to Park Sa-jin. Tae-oh reunites with Hye-won, investigating In-ju’s murder scene. Hee-ju discovers her father dead. In-ha learns Joong-mo knows he killed In-ju and is being removed from the inheritance. Joong-mo suffers a heart attack, and In-ha leaves him to die, but Hee-ju saves him. The family gathers at the hospital as Joong-mo is in critical condition. Tae-oh prepares a plan at the chairman's office. In-ha discovers a secret room indicating Tae-oh's presence. Tae-oh meets Prosecutor Ha, who retrieves incriminating evidence showing Gi-jun killing In-ju and Bona. The case is reopened, and Tae-oh turns himself in. In prison, Tae-oh's lawyer reveals a plan involving Gold H Investment. In-ha attempts to kill Joong-mo but is stopped by Tae-oh. Tae-oh confronts In-ha about his actions, but In-ha is unapologetic. Meanwhile, Mo Gi-jun awaits instructions from In-ha in prison. In-ha convinces Gi-jun to take the blame for the murders, then orders his assassination. Tae-oh's team plans Gold H Investment's strategy to protect Kang-oh's shares. Hee-ju tries to secure In-ju's wife's support for the Kang family. Tae-oh surprises everyone by appearing as Gold H Investment's co-CEO. Later, In-ha tries to intimidate Tae-oh. In-ju's wife proposes a partnership with In-ha. Tae-oh, Seong-ju, and Geum-suk join forces against In-ha. In-ha orchestrates Tae-oh's stepfather's release to harm Tae-oh's family. Geum-suk is arrested, and In-ha seizes power. Tae-oh mourns his mother's death. In-ha celebrates his newfound authority but is arrested for the murders. Tae-oh mourns his mother's death and revisits his past, realizing his journey with In-ha. He decides to protect Joong-mo and confronts In-ha. Seong-ju reconciles with his mother. In-ha's arrest shocks the shareholders. Tae-oh convinces Sa-jin to withdraw support from In-ha. In-ha is confronted by Gi-jun's testimony and faces charges. Joong-mo changes In-ha's surname and reveals his betrayal. In prison, In-ha reflects on his actions. Tae-oh meets Joong-mo and later visits In-ha, seeking closure. Hee-ju prepares to leave, while Tae-oh and Hye-won move on. In-ha's suicide follows. Three years later, Tae-oh becomes Kang-oh's chairman, and Joong-mo's project succeeds. The series concludes with Tae-oh's reflection on his journey.

Review "Impossible Heir" is a really exciting story about power, lies, and making things right. It keeps you interested the whole time! There are lots of different stories going on, like Tae-oh trying to fix a big problem and In-ha wanting to be in charge. The people in the story are interesting and have lots of different problems. You'll find yourself cheering for some and feeling sorry for others. It's all about who you can trust and who's going to come out on top. If you like stories with lots of surprises and interesting characters, you'll love "Impossible Heir"! "Impossible Heir" has its strengths, like its complex plot and interesting characters. However, it also has some weaknesses. The storyline can sometimes feel too convoluted, with too many subplots happening at once, which can make it hard to keep track of everything. Additionally, the pacing of the show can be inconsistent, with some episodes feeling rushed while others drag on. Some viewers may also find certain plot twists to be predictable or unrealistic. Overall, while "Impossible Heir" offers plenty of drama and intrigue, it could benefit from tighter storytelling and more consistent pacing.