Darius the Great Is Not Okay is a frame story in which 15-year-old Darius Kellner narrates a family trip to Iran that profoundly changed his life. Before his trip, Darius is insecure and feels unappreciated. His boss overrides his knowledge about tea-making, his classmates call him crude names and pull pranks on him, and his father, Stephen Kellner, criticizes his weight, hair, and awkward behavior. Darius has no real connection with his extended family in Iran because he’s only ever communicated with them via video calls over the computer. Darius, a lover of sci-fi and fantasy who makes frequent references to the classics of these genres, views the country of Iran and the universe of Star Trek in similar ways—as more of an idea than a real place. Darius is understandably anxious as he and his family travel to Yazd to visit his dying maternal grandfather, his Babou. 

However, once in Yazd, Darius easily falls in love with sweet, kind Mamou, his mother’s mother, who loves everything about Darius. But Darius has a harder time relating to Babou, a strong man and what Darius calls a True Persian. Shortly after arriving, Darius befriends Sohrab, a boy Darius’s age who lives near his grandparents. Sohrab is easygoing and invites Darius to play soccer with him and his friends. Darius recalls the only reason he stopped playing soccer back in America was because of his overly critical coach. Inwardly, despite his heritage, Darius doesn’t feel truly Persian because he’s only ethnically half-Persian, he’s never been to Iran, and he doesn’t speak Farsi. Yet, Darius tries to assimilate. Though his first soccer game with Sohrab and Sohrab’s friends Hossein and Ali-Reza goes well, Darius is devastated when his new friends mock him in the shower for being uncircumcised. Reminded of the bullies back home in Portland, Oregon, Darius’s depression is triggered as he once again feels inferior and different. Although several people try to cheer him up, it’s his father who finally succeeds in getting Darius out of bed. 

Darius is encouraged when, later, Sohrab arrives at Babou’s house and sincerely apologizes to Darius for bullying him. Darius accepts his apology, but Sohrab keeps apologizing even after Darius forgives him. Sohrab, who tends to believe people have negative motives, makes Darius feel secure by being persistent and sincere in his apology. Darius soon learns that Sohrab’s father is in prison for political reasons and wonders whether all Persian boys have father issues. 

Back at Babou and Mamou’s home, Darius continues feeling uncomfortable and unsure when trying to connect with Babou. Darius is intimidated by Babou’s ultra-masculine, overbearing personality. He is grateful for his own father’s support, but he feels wounded and betrayed when Stephen watches Star Trek with Darius’s little sister Laleh. Believing that their shared nightly Star Trek episode was his and Stephen’s only remaining point of connection, Darius feels replaced and excluded. 

On a family trip to visit the ruins of Persepolis and the palace of Darioush the Great, Babou stresses to Darius that his namesake was one of the greatest figures in Persian history. But the pep talk only makes Darius feel he’s a complete a disappointment in comparison. On the way back to Yazd, Babou gets lost driving home, exposing the full extent of his previously discretely managed illness to the whole family. Darius tries to comfort Babou by making tea, and Babou confesses that while he loves Stephen, Darius, and Laleh, it pains him that they will never be Zoroastrian or fully Persian. Darius feels hurt by this and thinks how unfair it is for Babou to criticize something that neither he nor his sister can control. 

Though they usually participate in the Nowruz celebration back in Portland, taking part in Yazd allows Darius to experience his Persian culture from the inside. As he does so, Darius comes to terms with the fact that he is both Iranian and American. He loves and appreciates both traditions and finds ways to cope with the misunderstandings and judgment he faces. On a trip to the Towers of Silence, Babou opens up again about how sad he is that his cultural traditions are fading away. Darius suddenly finds that he understands Babou’s lamentation.  

Meanwhile, Darius and Sohrab continue to develop a close bond, and Darius decides to get Sohrab a gift of a brand-new pair of football shoes. However, when Darius arrives at Sohrab’s house to give him the shoes, he finds a devasted Sohrab comforting his mother. The family has just learned of Sohrab’s father’s death in prison. A bereft Sohrab yells at Darius and tells him to get out. Darius flees Sohrab’s home barefoot, having taken his shoes off at the door, and runs through Yazd. He mentally berates himself for not wanting to spend time with his own father and for losing a true friend like Sohrab. Darius’s negative thoughts pile on and trigger a depression spiral.  

Stephen finds Darius, rightly intuiting where his son would go for solace after quarreling with his friend. As they sit together, Darius expresses his hurt that Stephen stopped reading to him when he was a child. Surprised Darius remembers, Stephen reveals that he went through a harrowing bout of depression and contemplated suicide when Darius was seven years old. When he finally came out of it, he didn’t think Darius wanted to hear his stories anymore. Stephen begins crying and confesses how guilty he feels that Darius inherited his depression. In a moment of closeness, Stephen brings up Sohrab, and Darius hints at deeper conversations that they aren’t yet ready to have, though a certain understanding passes between them. 

Unsure if Sohrab wants to see him, Darius gives his grieving friend space. As the Kellners pack for the trip home, Sohrab visits Darius at Mamou’s, concerned because Darius didn’t show up to play soccer like usual. Darius says he wasn’t sure if Sohrab wanted to see him and tells Sohrab he’s sorry about his dad. Sohrab apologizes for projecting his pain and anger onto Darius and gives him a birthday gift, a new pair of cleats. The two take a walk to their special park, and through conversation, they are able to mend their wounded friendship before Darius returns to the United States. Back at home, Darius feels more confident on the soccer field. He also stands up to a bully, makes a new friend, and has another heartfelt conversation with his father. The book ends with the Kellner family enjoying a pot of tea that Darius makes for them.