Billy Liar is a 1959 novel by Keith Waterhouse that was later adapted into a play, a film, a musical and a TV series. The work has inspired and been featured in a number of popular songs.

The semi-comical story is about William Fisher, a working-class young man living with his parents in the fictional town of Stradhoughton in Yorkshire. Bored by his job as a lowly clerk for an undertaker, Billy spends his time indulging in fantasies and dreams of life in London as a comedy writer.

Billy Fisher, the novel's protagonist and narrator, is a young man living with his parents and elderly grandmother in the Yorkshire town of Stradhoughton. He works as a clerk for local undertakers Shadrack and Duxbury, but has a lively imagination and has ambitions of becoming a writer. He has recently submitted some material to a London-based comedian, Danny Boon, and has received a vaguely encouraging response (inviting him to "call in for a chat next time you are in London") that Billy optimistically interprets as an offer of a job as a scriptwriter. Billy has a habit of telling lies – either to evade awkward situations, or simply for his own amusement – which have a tendency to backfire and embroil him in further difficulties. At other times, he finds escape in private fantasies (which he calls "No. 1 thinking"). In particular, he has invented, with a considerable amount of detail, a fictional land named Ambrosia, in which he is a war hero and/or prime minister. Among his other deceits, he had at the end of the previous year failed to post (in order to embezzle the postage money) over 200 promotional calendars for Shadrack and Duxbury. He is still trying to dispose of these.

The story follows events over a single Saturday in September. Billy gets up late (as usual), and faces criticism from his parents and grandmother. He goes to work at Shadrack and Duxbury, where he engages in friendly banter with fellow clerk Arthur Crabtree (including much use of exaggerated Yorkshire dialect), and more antagonistic exchanges with the other clerk, Eric Stamp. Billy and Arthur head out to the Kit-Cat cafe, where they find waitress Rita, to whom Billy had proposed marriage the previous evening. He now gives her an engagement ring – in fact belonging to his longer-term fiancee, Barbara (he has borrowed it back under the pretence that the size needed adjusting). At lunchtime, he meets up with Barbara: she likes to fantasise about their future family life in a cottage in Devon with "little Barbara and little Billy", but resists Billy's more amorous advances. In the afternoon, he returns to the office, despite it being a half-day, as he has submitted a resignation letter, and has a meeting scheduled with Mr Shadrack, one of the partners, to discuss it. Shadrack explains that he is not prepared to accept Billy's resignation until "one or two things" have been cleared up – including the matter of the calendars.

Billy returns home, to be chided by his parents and grandmother for having missed the family lunch. Later, he goes for a walk with Barbara. She is due to visit his home for lunch the following day, so he admits to having told her various lies about his family. He returns to the cafe with Arthur, and now gives Barbara's silver cross pendant to Rita. Billy and Arthur then visit the X-L Disc Bar, a record shop, where they meet Liz, Billy's other love interest, who has been away from Stradhoughton for five weeks.

In the evening, Billy goes to the New House, a pub where he performs a comedy stand-up turn; but his performance falls flat. He moves on to the Roxy, a dance-hall, where Arthur is performing more successfully as the singer with a local band. Billy again meets Liz, and tells her about his plans to move to London. She encourages him to take the plunge. Barbara spots her cross being worn by Rita, and starts an argument. Shadrack, who is also at the Roxy, tells Billy that further issues concerning his work have come to light, and that he is temporarily suspended from his job. There is an announcement over the tannoy system, repeated several times, that Billy is wanted on the telephone, but he ignores it.

Billy walks the streets of Stradhoughton with Liz. She recognises his flaws, but is prepared to tolerate them. At Foley Bottoms, a piece of open land, Liz proposes marriage to Billy, and he cautiously accepts. They make love – only to find they are being spied on by Stamp and two other youths.

Billy and Liz return to the Roxy to retrieve Liz's handbag, but Billy grows bored waiting outside and returns home. There his father tells him that it was he who had been trying to reach Billy by phone. His grandmother has suffered a fit and has been taken to Stradhoughton Infirmary, accompanied by his mother, who wants Billy to join them. Billy's father also reveals that he has found out about the calendars. Billy sets off in a taxi, having packed a suitcase with as many of the calendars as he can manage. At the hospital, he speaks to his mother, and tells her that he is going to London; but she is then called away to be informed that his grandmother has died.