Sitting by the window with views of the shining sea, a white-haired woman seals an envelope with trembling hands and thinks of her grandchildren – two sisters who haven't spoken for years. Will her final message bring them back together?

Ever since her sister Caitlin left the village of Heaven's Cove, Isla has cared for their beloved grandmother Jessie in her cosy red-brick cottage by the sea. Now, heartbroken after Jessie's death, Isla hopes to bond again with her sister. Until Caitlin insists she wants to sell the cottage they spent their childhood in.

But their grandmother, who always had a twinkle in her eye, had other plans. At her will reading the sisters are handed an envelope containing a cryptic riddle in Jessie's handwriting. Certain their grandmother, who loved puzzles and crosswords, wanted them to solve it together, Isla begs Caitlin for more time.

Then Isla meets tall, brooding Ben in the village, come from America seeking answers about his own family history. One of his ancestors was close to a relative of Jessie's… did Jessie mean for them to meet?

As Ben and Isla walk together on the wild Devon beaches, they discover a heartbreaking generations-old story of a woman who chose her family over true love. But Isla and Caitlin are no closer to solving their grandmother's riddle: and when Caitlin finally shares a shocking secret about her life back in London, selling their grandmother's home seems the only way forward.

Without their grandmother to guide them, will the sisters ever rediscover the meaning of family? Or will Isla be forced to leave Ben, and Heaven's Cove behind forever?