edited the summary of Duma Key Sunday, September 19, 2010.
The story begins shortly after a Minneapolis construction company owner named Edgar Freemantle barely survives a horrific on-site accident where his truck was struck and crushed by a crane. Though he survives, Freemantle's right arm is amputated, and severe injuries to his head cause Edgar to have problems with speech, vision, and memory. Because of the excruciating pain resulting from the accident and the subsequent recovery, Edgar also has violent mood swings and thoughts of suicide. After Edgar attacks his wife Pam twice – one time stabbing her with a plastic knife, the other strangling her – she files for divorce while he is still in recovery from his injuries.
On the advice of his psychologist, Dr. Kamen, Edgar takes "a geographical", a year-long vacation meant for rest and further recovery. He decides to rent a beach house on Duma Key, a (fictional) island off the west coast of Florida, after reading about it in a travel brochure. The beach house he is renting turns out to be place named Salmon Point, though Edgar nicknames it "Big Pink," because of its rich pink color. Also on the advice of Dr. Kamen, Edgar revives his old hobby of sketching after he settles in Big Pink. He settles into the house with the help of Jack Cantori, a local college student who buys his groceries, sets up his cable, and gets him whatever odds and ends he needs.
As Edgar becomes increasingly involved in his painting, it quickly becomes an obsession, with Edgar working with a furious energy and in a daze. Edgar's right arm begins to itch of phantom limb sensation and it forces him to bring up subconscious images in his paintings; he learns that his younger daughter, Ilse, is engaged to a choir singer and that Pam is having an affair with his former accountant, Tom Riley, by painting the aforementioned situations. Soon after this, Ilse comes to visit him. During this trip they reconnect and he paints The End of the Game, which he gives to her. While exploring the island they drive past an extraordinarily old looking woman, Elizabeth Eastlake, and Ilse later becomes violently ill as they drive into the overgrown part of the island. Elizabeth later calls Edgar, warning him that Duma Key is "not a place for daughters". Edgar initially disregards the message, since Eastlake has Alzheimer's disease.
During this time Edgar slowly recuperates by taking longer and longer walks along the beach. It is on one of these "great beach walks" that he slowly approaches and eventually meets and befriends a large man whom Freemantle had seen sitting under an umbrella off in the distance. This character, Jerome Wireman, to whom Edgar becomes quite close, is a hired companion for Eastlake. Edgar learns that Miss Eastlake is very wealthy and owns the entire island. He agrees to help Wireman care for her, and also reads poetry to her.
Edgar becomes more and more skilled in his painting the more he does it. The way he paints eventually becomes systematic: he gets a phantom-limb sensation, he paints a subconscious image, and develops an extreme appetite while doing so. He eventually compiles a large catalog of artwork and is convinced by his friends to try to sell it to an art gallery. He takes it to the Scoto Art Gallery, and it's manager, Dario, is extremely impressed and plans to exhibit Edgar's work. While the exhibition is being planned, Edgar discovers that his paintings have a subconscious power that allows them to manipulate events, places and people. This is evidenced when one of his paintings removes a bullet that was lodged in Wireman's brain from a previous suicide attempt, and another causes Candy Brown, a man accused of raping and murdering a young girl in a highly publicized case, to die suddenly in his prison cell. Despite this, Edgar's paintings continue to become popular, and two interviews of Edgar - one by Channel 6 news and another by Mary Ire, a prominent art critic and friend of Elizabeth Eastlake - turn Edgar into a local celebrity. With the exhibition looming, Elizabeth warns Edgar of the power of his paintings, and advises him that not only are they to be kept off the island - He had them in storage at the Scoto - but they all have to be sold to separate people, particularly his "Girl and Ship" series, which depict a haunted ship entitled the "Perse" and a girl that bears a striking resemblance to Ilse.
The exhibition of Edgar's work is held to great fanfare, and all of his family and acquaintances from his past life are in attendance. With the exception of "Wireman Looks West", which belongs to Wireman, and "Girl and Ship #8", which Edgar keeps for himself, all of the artwork that was on display sold, grossing more than $500,000 USD. Elizabeth Eastlake makes a surprise appearance at the exhibition, and warns Edgar of the danger of the paintings, telling him that the "table is leaking". Elizabeth dies of a violent seizure as she is trying to tell Edgar this, and Edgar suspects that the entity killed Elizabeth. In the aftermath of Elizabeth's death, Edgar reconnects with his daughters and seemingly reconciles with Pam, who he sleeps with at the upscale hotel she is staying at. However, when he returns to Duma the next day, after everyone leaves, he discovers that Big Pink was broken into and finds a canvas with "Where our sister?" sprawled on it, left in the house. He discovers that those in possession of his paintings either die, or become possessed by "Perse" and carry out her deeds, which mainly include killing people close to Edgar. Xander Kamen, who purchased a sketch, dies in the line at the local coffee shop of a heart attack. Tom Riley, who also bought a sketch, goes to kill Pam; However, on his way there he is involved in a horrific car accident that claims his life, thus preventing him from performing the deed. Most notably, Mary Ire, who had purchased one of the "Girl and Ship" paintings, breaks into Ilse's apartment and kills her by drowning her in her bathtub; Mary Ire commits suicide almost instantly thereafter. Edgar learns of these incidents from Pam, who angrily claims that she doesn't want to see him again, and blames him for Ilse's death.
Edgar begins to realize that his paintings are connected to tragic events in Miss Eastlake's childhood. Edgar discovers, through both his paintings and the drawings done by a young Elizabeth Eastlake after she had suffered a head injury and began drawing herself, that Elizabeth had inadvertently used her paintings to discover a figurine off of the coast of Duma Key. This figurine, of a red-cowled woman, used the young Elizabeth to begin changing the reality around her. Elizabeth tried to use her power to destroy the figurine by drawing it and then erasing it. This only enraged the entity Persephone, which then killed Elizabeth's twin sisters by leading them into the surf and drowning them. A young Elizabeth, with the help of her Nanny, eventually discovered that the entity can be neutralized by drowning her in freshwater, and Elizabeth was able to do this by placing the figurine in a cask that is sealed in a cistern under the original house on Duma Key.
Edgar, Wireman, and Jack travel to the Eastlake house, which is now overgrown by thick, unnatural vegetation. They manage to find the figurine, and are able to contain it in fresh-water inside one of their flashlights. Later, Edgar takes the flashlight back to Big Pink, where his daughter Ilse begins to form out of the sand and seashells under the house. The entity offers Edgar immortality and forgetfulness in exchange for the flashlight. Edgar, however, has a different flashlight and tricks the entity masquerading as his daughter to get close enough to him that Edgar can attack it with silver bracelets on his left arm. This attack destroys the entity's hold over his daughter. Later, Edgar makes a silver container (the figurine—and the entity—are vulnerable to silver), filled with freshwater, and then drops it into one of the freshwater lakes of Minnesota.
Edgar grieves for his daughter and says good-bye to Wireman, who was the sole beneficiary of Elizabeth Eastlake's will and, as a now very wealthy man, has decided to move down to Mexico and buy a hotel. Wireman extends an offer for Edgar to join him, and Edgar does move down to Mexico, but by the time he does, Wireman has already died of a heart-attack. The book ends with Edgar starting his final painting; a storm destroying Duma Key