Race to the Bottom of the Sea by Lindsay Eagar

Fidelia Quail is totally happy living with her marine biologist parents.  Even though she is only 11, she does her own field studies and even invents new technology to help with the work.  Then one day her parents are down in a submarine Fidelia designed when a terrible storm hits.  Fidelia feels that their deaths are partially her own fault, but she doesn't have much time to mourn.  Just months after their deaths, she is captured by some pirates who want her to use her inventions to get a treasure that has fallen to the bottom of a bay.  At first Fidelia is terrified, but after a while she begins to see her captors are more than ruthless pirates.

This was a remarkably original and emotionally complicated story.  It reminded me a little of Holes by Louis Sachar.  There are two stories going on in the narrative.  One is Fidelia's story and one is a story that began years before about the pirate and his one true love that he lost and desperately wants to find again.  Eagar fleshes out all the characters and shows how heroes can be villains, and villains can be heroic.  Readers should beware that there is some Biblical swearing in this one, as well as pirate violence and plenty of fish guts.  If anyone is a "Pirates of the Caribbean" fan, or just want a swashbuckling adventure, this one is definitely a good choice. (423p. 2018)