The following version of the book was used to create this study guide: Carofiglio, Gianrico. Three O'Clock in the Morning. Harper Collins Publishing, New York, NY, 2017. Kindle AZW file.

NOTE: In the novel, Antonio's parents are identified only as "Father"and "Mother" without a possessive name or pronoun. This guide adheres to the novel's syntax.

Antonio is a teenager as the novel opens. He hides the fact that he occasionally experiences minor seizures. One day he has an event at a friend's house, and the friend's mother alerts Antonio's parents. Later, Antonio has a more serious seizure at home. He is admitted to the hospital where he is diagnosed with epilepsy. The doctors provide a series of medications and order Antonio to modify his lifestyle. He quickly realizes the stigma attached to the disease means he needs to keep it secret. His parents take him to Marseilles in the hope that a specialist will provide a better treatment plan.

Three years later, Antonio has fallen into a routine of taking the pills twice a day and modifying his lifestyle to conform to the fact that he is an epileptic. When Father announces they are traveling back to Marseilles to see Professor Henri Gestaut again, Antonio dreads the trip but has no choice. His mother is delivering a paper so Antonio makes the trip with Father. They expect it to be a short trip but Professor Gestaut wants one final test before he declares Antonio cured – to stay awake for 48 hours without the anti-seizure medicine. Antonio and Father agree to the plan in order to get the all-clear, and they make arrangements to stay for two additional nights. Antonio is surprised when Father insists on staying awake as well and they set out to explore the city, including neighborhoods and places they would never have visited otherwise.

They are at a jazz club where Father takes the stage to play piano, surprising Antonio with his talent. They talk as they walk for hours, and Antonio is surprised to discover an affinity he had forgotten existed. The next day, they take a boat tour and meet two beautiful women who invite them to a party hosted by their friend Marianne. Antonio is struggling to stay alert and can tell Father is having the same problems. Marianne offers to be sure Antonio stays awake while Father has a short nap, and she and Antonio have sex. Though it is clear Father knows what happened, this is one of the few subjects they do not discuss.

They arrive for the final appointment with Professor Gestaut who declares Antonio cured. They sleep on the return flight to Italy. When Father drops Antonio off at the home he shares with his mother, Antonio feels their relationship has changed dramatically. Looking back on those events from more than 30 years later, Antonio felt they had plenty of time to recreate that connection, but they never did. Father died less than a year later.