Factory owner Larry Rains discusses plans with young architect Hilary Clarke. During the conversation, he is telephoned by his friend Pamela Siddell, an up-and-coming violinist.

Back in her studio, Hilary is rung by Sir Marshall Freyne, who asks her to discuss another project at short notice. Her office boy, Jimmy, calls a taxi - but is knocked down when hailing it. He is rushed to Queen Eleanor's Hospital with Hilary in attendance.

Sir Marshall turns out to be a governor of the hospital. Hilary asks for a letter of introduction, as she's decided to abandon her career in favour of nursing. Both Sir Marshall and the hospital's Matron try to dissuade her, but she is signed up to the full training course. Hilary is introduced to Sister and her colleagues, who explain the subtle differences in uniform and insignia. Nurse Christine Morris shows her the ropes.

Hilary gets on well with the patients and staff, especially the surgeon Mr Hervey, but she is criticised by Sister for numerous small infractions: talking to medical staff, running to fetch emergency supplies, feeding a diabetic the wrong diet and visiting young Jimmy without permission. Sister marks her down as a potential disciplinary problem, though privately regards her as quite promising - when ticked off for talking during lectures, Hilary goes on to name human bones perfectly.

Hilary helps Dr Barrett give a transfusion at Larry Rains' factory. Larry recognises her, assumes that she'd been called up and is surprised to hear that she voluntarily gave up her job. Their conversation is witnessed by Pamela, who is playing the violin in the factory. Later, while bidding her farewell, a machine explodes, badly injuring them both.

Larry wakes up in hospital, rambling deliriously. He recognises Hilary but can't remember why. A cracked rib has punctured his lung, and Hilary is asked to attend the operation, which is interrupted by an air-raid. Despite increasingly loud explosions, the operation continues and is a success.

Afterwards, Larry's rambling becomes more coherent, ending in a declaration of love for Hilary. He is baffled at the way she ranks her career over the prospect of love and marriage, but she's resigned to being an old maid.

Larry begins to recover his memory. Hilary attends to Pamela, who was also injured at the factory, who asks after him. She reports her condition to Larry, who writes her a letter. Hilary delivers this surreptitiously, but is caught by the ward sister. Hilary is transferred to a different ward.

On Christmas Day, Mr Hervey dresses up as Santa and invites Hilary to accompany him distributing gifts around the hospital, during which she stumbles across Larry and Pamela. Although Larry is stand-offish towards Hilary, Pamela is well aware of his feelings, and later tells him that she won't be accepting his proposal of marriage.

Christine is promoted to ward sister, and when enthusing about this to Hilary, Matron chides her for being over-familiar with her juniors. Hilary explodes with rage about petty regulations, and Matron summons her to her room and informs her that she has asked the Board of Governors to terminate her training.

Larry shows his gratitude to the hospital by making a large donation, but is shocked to discover how dependent British hospitals are on charity, especially if they cater for the poor. He asks the governors if the money can be spent on the nurses, but there are too many outstanding debts and expenses.

He is still in attendance when Hilary has her disciplinary hearing. She admits her guilt, but claims that the need for petty regulations arises from fundamental flaws in the British healthcare system that can only be cured by government reform, and urges the governors to use their influence. She pleads to be allowed to stay on. Larry says that he'll support her call for reform.

Later, Matron confesses to Hilary that she was similarly spirited at her age. Hilary's exam results put her near the top of the list, and her skills outweigh any disciplinary issues. Matron looks wistfully at a picture of her and Sir Marshall - an old flame - in a younger life, while Hilary returns to the ward.