Welcome to the most tumultuous summer of the 20th century. It's 1969, and for the Levin family, the times they are a-changing. Every year, the children have looked forward to spending the summer at their grandmother's historic home in downtown Nantucket. But like so much else in America, nothing is the same.

After a string of bad dates and no prospects, Sophia Othonos has finally hit the jackpot: an actual nice guy. When he suggests a romantic getaway, she’s sure they’re about to take the next step toward their future. A rustic cruise to the Galápagos Islands isn’t exactly her idea of a vacation, but Sophia is ready for anything…until her boyfriend has to cancel. Now she’s all alone on a trip that was meant for two. Sophia finds herself at a crossroads about who she is, what she wants, and whether her relationship is really everything she thought.

When Mallory Blessing's son, Link, receives deathbed instructions from his mother to call a number on a slip of paper in her desk drawer, he's not sure what to expect. But he certainly does not expect Jake McCloud to answer. It's the late spring of 2020 and Jake's wife, Ursula DeGournsey, is the frontrunner in the upcoming Presidential election. There must be a mistake, Link thinks. How do Mallory and Jake know each other?

After uprooting her life in the States, Irene Steele has just settled in at the villa on St. John where her husband Russ had been living a double life. But a visit from the FBI shakes her foundations, and Irene once again learns just how little she knew about the man she loved. With help from their friends, Irene and her sons set up their lives while evidence mounts that the helicopter crash that killed Russ may not have been an accident.

Fresh off a bad breakup with a longtime boyfriend, Nantucket sweetheart Lizbet Keaton is desperately seeking a second act. When she’s named the new general manager of the Hotel Nantucket, a once Gilded Age gem turned abandoned eyesore, she hopes that her local expertise and charismatic staff can win the favor of their new London billionaire owner, Xavier Darling, as well as that of Shelly Carpenter, the wildly popular Instagram tastemaker who can help put them back on the map.

Irene Steele shares her idyllic life in a beautiful Iowa City Victorian house with a husband who loves her to sky-writing, sentimental extremes. But as she rings in the new year one cold and snowy night, everything she thought she knew falls to pieces with a shocking phone call: her beloved husband, away on business, has been killed in a helicopter crash. Before Irene can even process the news, she must first confront the perplexing details of her husband's death on the distant Caribbean island of St. John.

On a perfect June day, Vivian Howe, author of 13 beach novels and mother of three nearly grown children, is killed in a hit-and-run car accident while jogging near her home on Nantucket. She ascends to the Beyond where she's assigned to a Person named Martha, who allows Vivi to watch what happens below for one last summer. Vivi also is granted three “nudges” to change the outcome of events on earth.

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.

Birdie Cousins has thrown herself into the details of her daughter Chess's lavish wedding, from the floating dance floor in her Connecticut back yard to the color of the cocktail napkins. Like any mother of a bride-to-be, she is weathering the storms of excitement and chaos, tears and joy. But Birdie, a woman who prides herself on preparing for every possibility, could never have predicted the late-night phone call from Chess, abruptly announcing that she's cancelled her engagement. It's only the first hint of what will be a summer of upheavals and revelations.