Finding Love on the High Seas by Stacy Eaton

Rainey Caldwell thrived on her work as a geneticist, even though she doesn’t like people. She prefers studying DNA to talking to a human. When it comes to social activity, Rainey is awkward and filled with anxiety. That feeling will only intensify when two old high school friends show up on the cruise ship that she’s stuck on for six days.
Zack Wheeler had been the most popular boy in school, but even thought things had looked great for him then, a lot had happened since. On the request of his family, Zach joins his buddies on a weeklong cruise and finds himself face to face with the nerdiest girl at school. Only she’s not a nerd now.
When Rainey and Zack decide to forget about the past, they look to enjoy the vacation, but when the ship docks, they are unsure what to do now with their newfound appreciation for each other.