The book starts in Ramsays’ summer house in the Hebrides (the islands near Scotland) just before the beginning of World War I. There the reader meet all the family: Mr and Mrs Ramsay, a couple who are around fifty years old, and their seven children. Some guests - friends and colleagues - come to visit Mr. Ramsay. One of these students is Charles Tansley, an awkward young man obsessed with his dissertation, who praises Mr. Ramsay as a metaphysical philosopher.
Across the bay from their house a large lighthouse is located. James Ramsay, a six-year-old boy, wants desperately to go to the lighthouse and asks if he can go there. His mother says that probably the weather would be good enough to visit the lighthouse. But Mr. Ramsay coldly responds that it is hardly possible. Charles Tansley agrees with him saying that weather is going to be bad. Having no support, the children resent their father and James even fantasizes about murdering him. They call Tansley by the nickname “Atheist” amongst themselves.
Another Ramsays’ guest is Lily Briscoe, a young and talented painter who starts a portrait of Mrs. Ramsay. Mrs. Ramsay thinks that Lily has not many chances to get married because of her personality. She likes her very much and, for Lily’s own good, tries to arrange their marriage with William Bankes, an old friend of Mr. Ramsay’s (who is almost twice as old as she is). The arrangement fails, Lily decides to remain single. Mrs. Ramsay, however, is happy by another marriage arrangement between Paul Rayley and Minta Doyle, two of their other guests.
During the afternoon some small bits of action happen. Willam Bankes talks to Lily about Mr. Ramsay but she is not really willing to hold a conversation. Lily begins painting the portrait of Mrs. Ramsay. Mrs. Ramsay herself soothes sad James and, eventually, Tansley who is worried about his shortcomings as a philosopher and turns to her for comfort several times. Tansley even shows a strange kind of affection towards her. Paul finally makes a proposal to Minta.
Meanwhile, Mr. Ramsay walks around the house and thinks about his mortality and things that he is going to leave to humankind. He asks Mrs. Ramsay to calm him, which she does. But then it’s her turn to worry about Paul, Minta and their relationship and also about Nancy and Andrew, her children, who are not yet back from the beach.
The Ramsays host a dinner party in the evening. Paul and Minta walk along the beach until the late evening searching for Minta’s brooch that got lost. The brooch is very precious to Minta because she inherited it from her grandmother. Paul plans to continue the search next morning. Two Ramsays’ children have helped them and also return late, so Mrs. Ramsay is angry. Charles Tansley offends Lily telling that women are unable to neither paint nor write. Mr. Ramsay reacts aggressively when another guest, a poet named Augustus Carmichael asks for an additional plate of soup. Things seem to go more and more wrong, but later, at night, all the mistakes seem to correct themselves and all the guests come together again to make it a good and memorable evening.
Mrs. Ramsay is finally happy. The food is delicious, she looks good and receives compliments. Mr. Bankes decides to stay for dinner and Paul’s proposal to Minta is accepted. After the party she puts her youngest children to sleep and goes to her husband to sit near him while he reads. Mr. Ramsay wants her to tell him that she loves him, but Mrs. Ramsey doesn’t do this. Though she smiles at him and says he was right and the weather will be bad tomorrow so they won’t be able to visit the lighthouse.
The second part of the book takes part some time after this evening. The World War I started. Mrs. Ramsay eventually died. Her oldest son, Andrew, served the military and was killed in the battle in France. His sister, Prue, married and died from a disease after giving birth to a child. Augustus Carmichael’s poetry suddenly becomes popular and brings him fame. Mr. Ramsay doesn’t know what to do without his wife who used to comfort him, praise him and calm down his fear and anguish regarding his work and philosophical problems.
The family no longer gathers in the summerhouse for a vacation. It falls into the state of disrepair: the garden is taken over by weeds and the house itself is a nest for spiders. It takes ten years for the family to return. Mr. Ramsay finally decides to make a trip to summerhouse with his daughter Cam and his son James. The trip almost fails because children aren’t ready for it but in the end they agree. The housekeeper, Mrs McNab, hires a few more women to help her repair the house and they manage to do this. The house looks good when Lily Briscoe also returns there.
Mr. Ramsay finally goes to the lighthouse with his children. They wake up very early and go to the boat to finally make the childish dream come true. The sailor McCalister and his son travel with them. The son of a sailor catches fish on their way. He cuts a piece of flesh from the caught fish for a bait and throws the wounded fish back into the water.
But the children are not as glad as they used to be. The lighthouse isn’t interesting for them anymore. They still resent their father for being egoistic and are adamant: Mr. Ramsay can do something for himself only.
Lily stays at home finishing the painting of Mrs. Ramsay she started at the beginning of the book. Via Lily’s thoughts we know that she didn’t marry anyone, but still has a strong friendship with William Bankes. Paul and Minta divorced. Lily remembers Mrs. Ramsay, some people said that she was too self-conscious and consistent, and even her beauty was too sharp. But still the reader can understand that Mr. Ramsey is sorely missed.
When Mr. Ramsey reaches the lighthouse with his children, he unexpectedly says that James steered the boat very well. James is puzzled, he didn’t expected a genuine compliment. They take the parcels for lighthouse keepers from the boat.
Lily finishes her painting (just as the sailing party reaches the lighthouse) and is satisfied with it. She observes the picture more and thinks that the completed work, a vision that came to life, means for her more than the idea of leaving a legacy to humankind.