Emma Hendricks is a strong, independent journalist known for getting at the truth. Needing to get away, she heads to Beacon Bay—a small coastal town in Maine—for the summer. After finding an antique bottle wedged between two rocks in the ocean, she frees it only to discover there's something inside.

Kathleen Connor is living in Beacon Bay during the 1940s in a time of war. Her husband runs the local store, but soon after their wedding, he begins to abuse her, turning her dreams into a nightmare.

Meanwhile, present day emergency room doctor and widower Logan Mayfield stitches Emmas hand. She shows him a faded, yellowed map with a coded message written at the bottom and signed, Until Tomorrow.

In a place far away and decades ago, Joseph Henry Rutherford III is serving his country the best that he can. Needing to connect with someone, he writes a long, heartfelt letter but it's mistakenly sent down the coast to Kathleen's address. The connection they form through letters creates a love they never imagined possible. When he returns from the war, they form a system of coded letters to secretly meet. When Emma's past catches up with her, will she fight for what she really wants?