A hopeless romantic ambivalent about his future in medical school falls for a hard-luck young woman who doesn’t believe in love.
Natasha Kingsley is set to be deported with her family back to Jamaica. As she spends the day trying to reverse the decision, she meets a charming would-be med student named Daniel Bae. He instantly falls for Natasha and believes that fate and destiny brought them together. They spend the day together and fall in love, but the thought of leaving and never seeing Daniel again causes Natasha distress.
Natasha meets with a lawyer, Jeremy Martinez, who tries to help her, but in the end, Natasha and her family must still leave. Daniel goes with her to the airport, and he forgoes attending Dartmouth as was his parents’ plan. By the end of their time together, Natasha and Daniel acknowledge their love for each other.
Five years later, Natasha and Daniel have gone on to attend good schools and lead the lives they want. They reunite in New York City when Natasha goes there for grad school with a student visa, and they agree to spend another day together.
The film starts with a voiceover from teenager Natasha Kingsley (Yara Shahidi) on the Big Bang and how it created the whole universe and the world we live in. She continues about how she thought it would take her whole life to understand the human heart, but for her, it only took a single day.
Natasha lives in New York City with her parents Samuel (Gbenga Akinnagbe) and Patricia (Miriam A. Hyman), plus her brother Peter (Jordan Williams). She has a keen interest in science and learning what she can. She also notes how her parents met when Samuel walked into Patricia’s store one day, and he, a hopeless romantic, fell for her. Unfortunately, she and her family are set to be deported back to Jamaica the next day. Natasha is determined to change this, so she makes an appointment with the immigration office to try and reverse their decision. She meets with an attorney, Lester Barnes (Hill Harper), and after asking questions, Natasha makes a tearful plea for her parents’ case, so Lester gives her a card to contact another lawyer friend of his, Jeremy Martinez (John Leguizamo), who can do pro bono work for her case. Natasha calls his office and is told that he is fully booked for the day, but after pleading, she is told she can meet with him for 15 minutes during his lunch break.
Daniel Bae (Charles Melton) is preparing for an interview for Dartmouth’s medical school program. He comes from a Korean family, and his parents Dae Hyun (Keong Sim) and Min Soo (Cathy Shim) encourage him to pursue a career as a doctor. He also has a brother, Charles (Jake Choi), who is a jerk to him.
Daniel and his friend Omar (Camrus Johnson) are on the same subway as Natasha, when it stalls for a moment. The conductor takes the time to reassure the passengers that everything is fine, and he brings up a story about a friend who missed a train on 9/11 and had he been on time, he would have made it into the city since he worked at the World Trade Center. He concludes his point with the notion that they are there for a reason and to “open your heart to destiny.” The guys get off at Grand Central Station, where Daniel spots Natasha and is instantly attracted to her. He also notices her jacket, which reads “Deus Ex Machina”, and since this relates to something he was reading about, he thinks he has to go after her.
Natasha is walking down the street while listening to music, unaware of a crazed driver on the street. Daniel sees him and rushes to catch Natasha before she walks into the driver’s path. She’s a little shaken up, so he sits to talk to her for a while. He believes in fate, but she doesn’t believe in anything that can’t be readily observed or proven. The two then go to a coffee shop before heading to their respective appointments, but Daniel gets a call saying his interview has been moved to the next day. When Natasha comes back, he tells her about a survey that was taken between couples to determine whether they truly love each other. He asks Natasha some questions to try and woo her, but she thinks it’s corny.
Daniel escorts Natasha to Jeremy’s office, which happens to be in the same building where Daniel is set to have his interview. Natasha goes in and is told by Jeremy’s assistant that he got clipped by a car (probably the same one that almost hit her) and is in the hospital, so his next free time is around 4:30. With more time to kill, Natasha agrees to keep hanging out with Daniel.
The two make a stop at a hair/wig shop that Daniel’s parents own. He explains to Natasha how Koreans have business with manufacturing and distributing wigs. When they get there, Charles makes fun of Daniel in front of Natasha, while Dae Hyun comes in and is more pleasant to Natasha. They leave, with Daniel feeling embarrassed.
Natasha and Daniel continue to spend the afternoon together, going to a planetarium and making conversations about stars. Daniel notes that he writes poetry, and Natasha suggests what he could write about, including the stars. They later go to a spot where Daniel sings “Crimson and Clover” to Natasha before they have their first kiss. One of them even imagines a life together, with marriage and a son in their future. However, Natasha is running late for her appointment with Jeremy, and when Daniel sees she is upset, she reveals to him that she is going to get deported, and that is why all of this is going to feel painful for her. She goes and meets Jeremy, where he offers to set up a new trial for her parents’ case for the next day.
Daniel goes back to the shop where he and Charles get into a physical fight before their father breaks it up. After calming down, Daniel narrates a bit of his family’s history, and how he and his brother have both Korean and American names. After he’s gone, Natasha goes to the shop and asks Charles for Daniel’s number. After seeing that she really likes him, Charles does so. She calls him, they reunite, and spend the rest of the day together before falling asleep in Central Park.
The next morning, both Natasha and Daniel rush to their appointments, but first Natasha has to call her parents to let her know she is safe. Daniel interviews for Dartmouth with Jeremy, but Natasha barges into the office and asks what the verdict was. Jeremy somberly reveals that Natasha’s case was rejected, and she and her family must still leave that day. She is angry and vents to Jeremy before leaving, and Daniel cuts the interview short to go after her. He walks her home and meets her family before they head to the airport.
While there, just before having to say goodbye, Daniel does one more test from the survey he mentioned earlier in which the couples have to maintain direct eye contact for four minutes without a word. In between this, we see Natasha leaving and going back. Flashforward to the future where Natasha is doing fine in Jamaica and goes to a good school, while Daniel has decided to attend Hunter College instead while working a job he is more comfortable with. The four minutes ends, and Natasha tells Daniel she loves him. He tearfully says his test worked, and that he loves her too.
Five years later, Natasha has returned to NYC for grad school, as her student visa has been approved. She meets Jeremy in the same coffee shop that she went to with Daniel to tell him what she has been up to, and learns that the doctor who treated him on the day they met would later become his wife. When she asks him about Daniel, Jeremy says he hasn’t seen him since the interview, and Natasha can’t find him anywhere on social media. After Jeremy leaves, Natasha prepares to leave too, unaware that Daniel is in the same shop about to read a poem. She hears his voice, and they see each other. He walks up to her and asks to spend the day with her, but she only has about an hour to spend. He is okay with that, and they kiss.