The Codebreaker's Secret by Sara Ackerman

A brilliant female codebreaker. An "unbreakable" Japanese naval code. A pilot on a top-secret mission that could change the course of WWII. The Codebreaker's Secret is a dazzling story of love and intrigue set during America's darkest hour.
1943. As war in the Pacific rages on, Isabel Cooper and her codebreaker colleagues huddle in "the dungeon" at Station HYPO in Pearl Harbor, deciphering secrets plucked from the airwaves in a race to bring down the enemy. Isabel has only one wish: to avenge her brother's death. But she soon finds life has other plans when she meets his best friend, a hotshot pilot with secrets of his own.
1965. Fledgling journalist Lu Freitas comes home to Hawai'i to cover the grand opening of the glamorous Mauna Kea Beach Hotel, Rockefeller's newest and grandest project. When a high-profile guest goes missing, Lu forms an unlikely alliance with an intimidating veteran photographer to unravel the mystery. The two make a shocking...