Janet King owns a flower shop which earns her a comfortable income, thanks to the patronage of Lord Camber, whom she has never met. Lord Camber is a philanderer and his current conquest is Shirley Neville, a famous musical comedy star, but, as John Betterton, he has also captured the heart of Janet King - and fallen in love with her.
Shirley and Camber seem ill-suited - they bicker and quarrel endlessly, but Shirley really loves him and inveigles him into proposing marriage. Camber gives Janet the order for the wedding flowers, but cannot bring himself to tell her the truth, sending her a letter and a farewell present instead. He and Shirley set off on a world trip, while Janet, broken-hearted and still unaware of Betterton's true identity, gives up the flower shop to become a nurse in a children's hospital.
She attracts the attention of Dr. Napier, a famous Harley Street physician who has a reputation for sternness and bad temper, but Janet stands up to him - much to his secret delight. He employs her at his private nursing home and also as his laboratory assistant, and soon they are falling in love with each other.
One day a new patient arrives - it is Lady Camber, accompanied by her legal adviser Sir Bedford Slufter and Peach, who used to dress her at the theatre. Shirley is suffering from a weak heart. When Lord Camber arrives to see her, he comes face-to-face with Janet, who recognises him as John Betterton and is appalled at his deception. Although she tells him plainly she no longer feels anything for him, he persists in telephoning her every minute of the day. Peach becomes suspicious and, jealous of Shirley's growing affection for Janet, persuades her mistress that Camber is having an affair with the nurse. Shirley tricks Camber and Janet into joining her at her bedside, and after accusing them of being lovers, she collapses.
Dr. Napier is furious, having forbidden Camber to see Shirley. He hears Peach's suspicions and accuses Janet of betraying his love for her, as well as failing a sick woman and her duty as a nurse. Shirley never recovers from the collapse - she drinks a medicine given to her by Janet, and dies. Sir Bedford and Dr. Napier are suspicious about the cause of death and Sir Bedford accuses Janet outright of poisoning Shirley, having seen her replace a bottle of poison in the medicine cabinet. Napier, however, tackles Camber and tricks him into confessing to his wife's murder and taking poison himself. Janet then confesses that she saw Camber add the poison to the medicine, and she threw it away. Camber is furious, believing he has thrown away his life for nothing, but Napier tells him he has drunk nothing worse than water.
Camber is humiliated and flees the nursing home, leaving Janet and the doctor to plan their future together.
