Ambrose Ashley is the owner of a large country estate on the Cornish coast and has been guardian to his orphaned cousin Philip since he was seven years old. On Sundays, Philip's godfather, Nick Kendall, and his daughter Louise come to lunch with them, as do the Reverend Pascoe and his family. Life is good apart from a few health problems that require Ambrose to spend the winter in warmer climates. As the damp weather approaches, he sets off for his third winter abroad and chooses Italy.
By the time he has reached his twenties, Philip misses Ambrose on his sojourns in Italy but regularly receives letters from him. Ambrose writes that he has met a cousin of theirs called Rachel in Florence. In the spring, Ambrose says that he and Rachel are married and have no immediate plans to return to Cornwall. Gradually, the tone of Ambrose's correspondence changes. He complains of the sun, the stuffy atmosphere of the villa Sangalletti, and terrible headaches. In a letter that reaches Philip in July, Ambrose says that a friend of Rachel's called Rainaldi has recommended that Ambrose see a different doctor. Ambrose says he can trust no one and claims that Rachel watches him constantly.
Philip discusses the contents of the letter with his godfather Nick, who is his guardian until his coming of age at 25. Nick suggests that Ambrose may be suffering from a brain tumour. Philip travels to Italy and reaches the villa Sangalletti, where he learns that Ambrose is dead and that Rachel has left the villa. When Ambrose returns to Cornwall, Nick tells Philip that he has received a communication from Rainaldi, containing two pieces of information: the death certificate confirms that Ambrose's cause of death was a brain tumour, and, as Ambrose had never changed his will in Rachel's favour, Philip is still heir to the estate.
Two weeks later, Nick receives word from Rachel, saying that she has arrived by boat at Plymouth. Philip invites her to stay with him, and a harmony develops between them. One day, a tenant from East Lodge gives Philip a letter from Ambrose, written three months before his death. In it, Ambrose tells Philip about his illness and talks of Rachel's recklessness with money and her habit of turning to Rainaldi rather than himself. Finally, he wonders if they are trying to poison him, and he asks Philip to come to see him. Rachel later shows Philip an unsigned will that Ambrose wrote in which he leaves his property to Rachel. Philip begins to trust Rachel again.
On the day before Philip's 25th birthday, he prepares to transfer Ambrose's estate to Rachel. He also gives her the family jewels, and they make love. The next day, Philip announces that he and Rachel are getting married, but she denies this in front of friends. Not long afterward, Philip falls ill for many weeks, during which Rachel nurses him. When he is well enough to go outside, he finds that the terraced gardens are complete and that work has begun on a sunken garden. The foreman tells Philip that the bridge over the garden is a framework and will not bear any weight.