Student doctors arrive at St. Swithin's Hospital to begin their training at the start of a new term. These include new students, such as Simon Sparrow, and those that have previously failed their final exams, such as Tony Benskin, Richard Grimsdyke and 'Taffy' Evans.

After the Dean of the hospital has addressed the students in the lecture theatre, Simon meets Grimsdyke; in the hospital bar, Grimsdyke introduces the shy new student to his friends Benskin and Evans.

Simon rents a room at a guesthouse, where he is the unwilling recipient of the romantic advances of the landlady's daughter. Once his training has begun and he has obtained books and equipment, he hands in his notice at the guesthouse and moves into a shared flat with Grimsdyke, Benskin and Evans.

The term continues as the trainees pursue various studies. At the end of the second year, they take exams. With these out of the way, Grimsdyke decides that Simon needs a girlfriend, and arranges a date for him with one of the staff nurses. Simon is not keen on the idea, and the date is an embarrassing failure.

The third year begins with the students undergoing clinical training in the wards, under the stern gaze of Sister Virtue. Later, when a woman falls over in the street outside the hospital, Simon goes to her aid and, with Grimsdyke's encouragement, is provided with another opportunity to set up a date. Borrowing a suit, he arranges to meet her at a restaurant. But the high prices mean that he has to concoct an elaborate excuse to rush away without buying a meal.

Later, at the hospital, fiery surgeon Sir Lancelot Spratt arrives to teach students how to examine patients prior to surgery. In the ward, Simon makes eye contact with nurse Joy Gibson, and is distracted from Sir Lancelot's teaching. When Grimsdyke learns of this, he convinces Simon to ask her out on a date, though Simon is initially reluctant. But after a shaky start, the date goes well, and a romance begins.

Assisting Sir Lancelot Spratt in the operating theatre, Simon passes out at the sight of blood. He is dragged away and brought out on a stretcher, to the amusement of his friends. Joy is sympathetic, however, and offers him words of encouragement.

As the fifth and final year of study starts, the romance between Simon and Joy continues. Meanwhile, Christmas Eve presents Simon with his first opportunity to deliver a baby, which the proud mother names after him. As he leaves, Simon realises the value of his chosen vocation.

As term progresses, St. Swithin's beats St. Crispin's to win the Hospitals Rugby Cup. By way of retaliation, students from St. Crispin's steal the St. Swithin's mascot, a stuffed monkey. Simon and his friends are involved in the frantic chase to recover the mascot. Flour bombs are thrown and good-natured brawling ensues. After pursuing students from St. Crispin's in an ambulance, Simon and his friends are arrested by the police and fined by a magistrate. They do not have the money to pay. Spratt, a keen rugby fan, takes pity on them and pays their fines.

As final exams approach, Simon gets into trouble after he accidentally falls through a skylight into Sister Virtue's bedroom following a late-night date with Joy. Because of this, the dean of St. Swithin's expels him; however, Spratt, confident that Simon will make a good doctor, reminds the dean of his own student transgressions and convinces him to give Simon another chance.

Simon and Evans pass their final exams; Grimsdyke and Benskin do not. On his first night as a doctor, in the middle of celebrations at the hospital bar, Simon is called away to provide cover in the short-staffed casualty department. Joy proudly watches as he walks away and awaits his return.