Bert, a power station electrician, accosts Nell, a shop worker, on a busy London Underground train. She spiritedly fends off his attentions but he tells her they are meant to be together. After leaving the carriage, Nell drops one of her gloves and Bill, a young Underground attendant, returns it to her. Like Bert, Bill is clearly entranced by Nell.

Later that day, Bill searches the rush-hour crowds for Nell. When she appears, he asks her to go on a date with him at the weekend. She agrees and they say goodbye, watched by a jealous Bert. As Bert returns home he is greeted by Kate, a dressmaker who lives in the same building. She is devotedly in love with him, but Bert callously tells Kate that their relationship is over.

That weekend Bert bumps into Nell, who is on her way to meet Bill. Bert forces himself upon her and she angrily pushes him away. Despite this he tells Nell he will marry her one day. She and Bill share an enjoyable day, and Bill asks Nell to marry him. This time she says yes. As Bill drops Nell off at home, she mentions that Bert also proposed to her that day.

In the pub, Bert boasts about his 'relationship' with Nell. Some men decide to stir up trouble by telling Bert that Nell is in love with Bill, not him. When Bill enters, Bert picks a fight with him, but loses. Replaying the fight over and over in his mind, an angry Bert returns home and asks Kate to do him a favour.

The next day, Kate prowls the busy Underground. She approaches Bill and pretends to feel faint. When he takes her to a secluded corner to recover, Kate pretends that Bill has attempted to assault her. A large crowd gathers, including Nell, and Bill is taken away to be questioned.

Bert sends Nell a letter, renewing his proposal of marriage. However, Nell sees Bill in the street and tells him she has decided to believe his version of events. They discuss the fact that if Kate does not tell the truth Bill will lose his job and he and Nell will not be able to get married. When Kate comes to Nell's haberdashery to buy some material, Nell contrives to find out her address. She compares it to her letter from Bert and realises that Kate lives in the same house. Nell goes to confront Kate, narrowly avoiding Bert, who has packed his bags intending to leave Kate and start a new life. Kate refuses to confess that she lied about Bill until Nell shows her the letter from Bert.

After Nell leaves, Bill turns up to confront a tearful Kate. He accompanies her to the power station where Bert works. While Bill talks to Bert's employers, Kate rushes to find Bert, whom she still loves. In anger he strikes her, causing an electrical failure in the process. Bert runs away and a chase ensues, with Bill finally trapping Bert in an Underground lift.

Time passes and daily life on the Underground continues as before. Nell gazes lovingly at Bill, now her husband, as he goes about his work on the train.