Charles Arrowby has had a successful career in the London theater, as actor, playwright and director, but suddenly, at middle age, he decides to retire and become a recluse. He buys a remote house "Shruff End" on the rocks by the sea, a somewhat creepy place without electricity and other amenities, outside a small village. Seeking for peace and starting to write his reminiscences, fate has a new drama in store for him when he unexpectedly bumps into his childhood sweetheart, Hartley. She is now a plain housewife with a worn-out face, but the spark of love is rekindled in him. Not in her, by the way, as she was the one who left him in the past.
Hartley is married but seems not entirely happy with her simple husband Ben and Charles begins stalking her and sets his heart on destroying her marriage. His obsession grows to such ludicrous heights that he even kidnaps her and keeps her for several days prisoner in a small, windowless room in his rickety house. Hartley, however, makes perfectly clear that she is not interested, she has her own life, and her marriage may not be perfect, but it is her choice. At the heart of the novel lies Charles's inability to recognize the selfishness and egotism that propel him to these romantic shenanigans - also in the real world he behaves like a theater director who thinks he can "stage" the lives of the people around him. He projects his own thoughts on others and does not realize that they may have a will of their own.
In the meantime, Charles' eccentric London friends have also started arriving, one after the other, to keep him company. He has never married, but there are a few ex-lovers who make their appearance again. Two such women are the actresses Lizzie and Rosina, who are still obsessed with Charles. In the past, Charles has broken up the marriage between Rosina and another actor, Peregrine, and then cruelly dropped her - showing how destructively the one-sided love of Charles works out on his relations. Peregrine also appears (and happens to find an opportunity for revenge), and another friend, Gilbert, who for a while acts as Charles' "house slave."
Washing up in Charles house is also the adopted son of Hartley, Titus, whom Charles tries to use as a tool to get closer to the woman of the dreams of his youth. But Titus proves to be a person with a strong mind of his own. Finally, there is Charles nephew James, with whom he has always felt some kind of competition. James is a sort of guru (we are in the 1970s after all) with vague Eastern / Buddhist leanings. But he is a crucial figure as he not only literally saves Charles' life, but also sets him on the path to realizing his follies.
Charles is not a wholly pleasant person. He is obstinate (we already see this in the way he writes about his ridiculous recipes in the beginning of the book), egoistic and dictatorial. A mitigating factor is that he has romantic ideals, but unfortunately these are directed in the wrong way. Charles tells the story, but the reader has to be careful for he is - as all narrators in modern literature in fact are - not very reliable. With the character traits outlined above, he is constantly whitewashing his actions and his own thoughts and preferences seem to constitute the whole universe.
Happily there is also a more pleasant protagonist in the book: the sea of the title. It is always present with its various moods, mysterious (Charles once imagines he sees a dragon) but also a practical place for exercise, and in the end both life-taking and life-giving. The Sea, the Sea is a rich tapestry with interesting characters and deep philosophical connotations. Some reviewers have called the central story of Charles' obsession difficult to believe, but love is obsession, isn't it?