Message in a Bottle is a novel by acclaimed novelist Nicholas Sparks. In this novel, Theresa Osborne is still grieving the sudden end of her eight year marriage when she finds a bottle on the beach that contains one of the most touching love letters she has ever read. When Theresa publishes this letter and discovers others, she decides to meet the romantic author. Soon Theresa and Garrett Blake find themselves wrapped in a passionate affair that is marred only by distance and Garrett's continued devotion to his deceased wife. Message in a Bottle is a beautiful love story that deals with the difficult subjects of grief, loneliness, and surviving despite tragedy.

Theresa Osborne, on a rare vacation, is running on the beach, thinking of the demise of her eight year marriage and the difficulties of dating with a twelve-year-old son at home. Theresa admits to herself that she is lonely, not because she misses her husband specifically, but because she misses the companionship inherent to marriage. As these thoughts are going through her mind, Theresa sees a bottle on the beach. Inside is one of the most touching love letters Theresa has ever read, apparently a letter from a man to his lost love. When Theresa shows the letter to her friend and editor, she is talked into publishing the letter in her parenting column in the Boston Times. The reaction of the readers is overwhelming and Theresa returns from vacation to piles of letters and many phone calls from people wanting to know more. One of these phone calls comes from a woman claiming to have another letter written by the same man.

Theresa is fascinated with the letter and decides to do some research on messages in bottles. In an article of the subject, Theresa finds a third letter quoted. Theresa convinces this man to give her copy of the letter. Then Theresa takes all three letters to her editor and together they use the information in the letters to locate Garrett Blake, the author. Deanna, Theresa's editor, talks her into going to Wilmington, North Carolina to check Garrett out for herself, if for nothing but to satisfy her curiosity. Theresa reluctantly agrees and finds herself on a plane the following day.

When Theresa arrives in Wilmington, she goes to Island Diving, Garrett's diving shop. At the shop, Theresa sees a picture of Garrett and reads several articles about his diving career and the wood hull boat he restored with his wife the year before her death. From there Theresa visits the boat, Happenstance, and runs into Garrett. Garrett is drawn to Theresa for reasons he cannot explain and decides to take Theresa for a sail on Happenstance. This sail leads to lunch the following day, then dinner, and soon Theresa and Garrett find themselves inseparable.

Theresa and Garrett spend four days together before Theresa must return to Boston. Three weeks later, Theresa brings her son, Kevin, to visit Garrett. Garrett teaches both Kevin and Theresa to scuba dive, helping them to get their certification. After that visit, Garrett and Theresa find their time together to be sporadic and difficult to arrange. Theresa finds herself canceling a trip to see Garrett at Thanksgiving, a visit his father had looked forward to because it would be their first meeting, in order to go to a meeting with syndicate representatives who might be interested in picking up her column.

When Garrett sees Theresa next, he learns that her column has been picked up by one of these syndication companies and that her career will be taking a more demanding course. Garrett asks Theresa to give it all up and move to Wilmington to be with him. Theresa becomes upset, unsure that Garrett is offering her more than a love affair doomed to end. Theresa leaves the apartment to clear her head. Garrett goes into Theresa's bedroom to search for paper, wanting to write down his feelings in a way that he believes will help him express them clearer. Instead of paper, Garrett finds three of his letters that he dropped into the sea. When Garrett questions Theresa about the letters and learns that she published one of them, he becomes convinced that she concocted a scheme to meet him and seduce him. Garrett leaves in anger.

Theresa follows Garrett to his home in Wilmington and explains what happened with the letters. Instead of making up, however, Theresa tells Garrett that she does not believe he can ever forget Catherine, his deceased wife, and she cannot live in that shadow for the rest of her life. Theresa suggests that they end their relationship now, before either of them can be hurt any deeper. Theresa drives away despite the fact that Garrett attempts to chase her down and stop her. A few days later, Theresa gets a call from Garrett's father asking her to return to Wilmington. Jeb tells Theresa that Garrett died when he went sailing during a storm. His body washed ashore and they are able to bury him together.

A week or more later, Theresa finds a package from Garrett waiting for her. Theresa opens it and discovers a bottle with a message inside. The letter tells her that Garrett has finally realized that Catherine has brought them together and it is time for him to let her go. Garrett also says in the letter that he went out on Happenstance that day to send one final letter to Catherine before devoting his life to a relationship with Theresa and Kevin. A year later, Theresa sends a letter to Garrett via a message in a bottle, thanking him for coming into her life and teaching her that she can go on despite her overwhelming grief.