The story revolves around the life of Jonathan Dakers, a small town doctor. He is training to be a surgeon when his father dies. Due to the resulting financial problems, he cannot continue his training. He buys a share in Dr. Hammond's general practice in Wednesford, a poor foundry town. When Dakers notes that many patients have been injured in industrial accidents at the foundry, he comes into conflict with its owner Sir Joseph Higgins, and the owner's son-in-law Dr Craig, who owns the town's competing medical practice. He writes a report criticising the condition of the foundry and buildings the workers live in but Craig, who is also the local Health Officer, deliberately mislays it. When Dakers performs a life saving tracheotomy on a child with diphtheria, and takes the child to the hospital, he is charged with misconduct, as the hospital charter precludes infectious cases. As a child Jonathan Dakers met Edie Martyn. Years later they meet again when he is training in a hospital. He becomes infatuated with Edie; however, she begins a relationship with his brother Harold, who is killed in the First World War, leaving Edie pregnant. To save her from shame Jonathan marries her, despite being in love with Rachel Hammond, the daughter of his medical partner. Soon after giving birth to a son, Edie dies, first telling Jonathan to be happy with Rachel, whom he later marries.
The film was a big hit on release, being the third most popular movie at the British box office in 1948. It led to Michael Denison being voted the 6th most popular British star. According to Kinematograph Weekly the 'biggest winner' at the box office in 1948 Britain was The Best Years of Our Lives" with Spring in Park Lane being the best British film and "runners up" being It Always Rains on Sunday, My Brother Jonathan, Road to Rio, Miranda, An Ideal Husband, Naked City, The Red Shoes, Green Dolphin Street, Forever Amber, Life with Father, The Weaker Sex, Oliver Twist, The Fallen Idol and The Winslow Boy''. Michael Balcon later claimed the film earned £1,041,000 at the UK box office of which £416,000 went on the entertainment tax, £375,000 went to exhibitors and £57,000 to the distributors, meaning the makers of the film did not recover their costs from the UK release.