Content Warning: This section of the guide contains depictions of the death of a young person and the nonconsensual recording of a kiss.

Martha Boyle is the 12-year-old main character and the protagonist of Olive’s Ocean. After receiving a journal entry written by the deceased Olive Barstow, Martha and her family visit Martha’s grandmother in Cape Cod for summer break. There, she bonds with her grandmother, forms a crush on Jimmy, is betrayed by her crush, and returns home with a newfound resolve to connect with Olive through the seawater she retrieves from the ocean. Martha has a revelation while collecting the seawater and nearly drowning—she realizes she is not the central focus of everyone’s world, and the world will go on with or without her. Understanding this helps her to process Olive’s death and her grandmother’s aging, and it puts her mind at ease about many of her present conflicts, which now seem small.

While Martha is the protagonist, she’s not the titular character of the story. Henkes gives the title to Olive Barstow. The narrative belongs to Martha, but Martha is inseparable from the deceased Olive, who she learns from and about as the story progresses.