Yesterday's Tides by Roseanna M White

In 1942, Evie Farrow is used to life on Ocracoke Island, where every day is the same--until the German U-boats haunting their waters begin to wreak havoc. And when special agent Sterling Bertrand is washed ashore at Evie's inn, her life is turned upside down. While Sterling's injuries keep him inn-bound for weeks, making him even more anxious about the man he's tracking, he becomes increasingly intrigued by Evie, who seems to be hiding secrets of her own. Decades earlier, in 1914, Englishman Remington Culbreth arrives at the Ocracoke Inn for the summer, but he doesn't count on falling in love with Louisa Adair, the innkeeper's daughter. When war breaks out in Europe, and their relationship is put in jeopardy, will their love survive? As Evie and Sterling work to track down an elusive German agent, they unravel mysteries that go back a generation. The ripples from the Great War are still rocking their lives, and it seems yesterday's tides may sweep them all into danger again today.

This is definitely one of the better dual timeline books out there; the two timelines are closely connected through location, characters, and wartime setting. So often my complaint with dual timelines is that they feel like two completely separate stories mashed together (and rarely with equally interesting storylines), but these two timelines resonate and feel cohesive. I'll be honest, I still wish it had been a two book series instead of a dual timeline; that way we'd get more story and each timeline could have been fleshed out more (for instance, I feel like we still never really know all that much about Sterling, even at the end). But wishing for more story is often how I feel after reading a dual timeline.

The WWI timeline is certainly the more active one, full of name-drops of characters from other series by the author (though I'm not sure how I feel about there being so incredibly many), and it feels like it has much higher stakes, both relationally between Louisa and Rem and physically as action heats up in Europe. The WWII timeline is slower paced, with more to say on grief and healing through it. 

Thank you Bethany House and NetGalley for the complimentary e-book. I was not required to write a positive review, and all opinions are my own.

All (well, most of) the related books, in chronological order:

The Culper Ring:
1. Ring of Secrets
1.5. Fairchild's Lady (novella)
2. Whispers from the Shadows
2.5. "A Hero's Promise" (short story)
3. Circle of Spies

Edwardian/WWI Era:

Ladies of the Manor
1. The Lost Heiress
2. The Reluctant Duchess
3. A Lady Unrivaled

Shadows Over England
1. A Name Unknown
2. A Song Unheard
3. An Hour Unspent

The Codebreakers
1. The Number of Love
2. On Wings of Devotion
3. A Portrait of Loyalty