Nantucket writer Madeline King couldn't have picked a worse time to have writer's block. Her deadline is looming, her bills are piling up, and inspiration is in short supply. Madeline's best friend, Grace, is hard at work transforming her garden into the envy of the island with the help of a ruggedly handsome landscape architect. Before she realizes it, Grace is on the verge of a decision that will irrevocably change her life. Could Grace's crisis be Madeline's salvation?

With rumors of infidelity straining Greg and Tess MacAvoy's marriage, the couple head out on their sailboat one early summer day to celebrate their wedding anniversary, hoping the roughest waters are behind them. But in an accident off Nantucket, they mysteriously drown, leaving behind two small children as well as three couples who have long been their closest friends. Tragedy brings to the surface long-simmering conflicts and emotions, and the MacAvoys' six grieving friends find themselves unprepared for the revelation of secret upon secret.

Hollis Shaw, creator of the popular food blog, Hungry with Hollis, is shocked when her heart surgeon husband, Matthew, is killed in a one-car accident on a snowy morning. The cracks in Hollis’s perfect life—her strained marriage and her complicated relationship with her daughter, Caroline—grow deeper. So when Hollis hears about something called a “Five-Star Weekend”—one woman organizes a trip for her best friend from each phase of her life: her teenage years, her twenties, her thirties, and midlife—she decides to host her own Five-Star Weekend on Nantucket.

Kelley Quinn is the owner of Nantucket's Winter Street Inn and the proud father of four, all of them grown and living in varying states of disarray. Patrick, the eldest, is a hedge fund manager with a guilty conscience. Kevin, a bartender, is secretly sleeping with a French housekeeper named Isabelle. Ava, a school teacher, is finally dating the perfect guy but can't get him to commit. And Bart, the youngest and only child of Kelley's second marriage to Mitzi, has recently shocked everyone by joining the Marines.

The Carmichaels and the Grahams have gathered on Nantucket for a wedding. Plans are being made according to the wishes of the bride's late mother, who left behind The Notebook: specific instructions for every detail of her youngest daughter's future nuptials. Everything should be falling into place for the beautiful event - but in reality, things are far from perfect. While the couple-to-be are quite happy, their loved ones find their own lives crumbling.