Lucy’s best friend and neighbor, known for his love of science and jazz music, who frequently uses his inhaler due to asthma.

Lucy’s father, a scuba diver, detective, and photographer, who initially struggles with grief following his wife's death.

A shark biologist and Lucy’s mother, whose adventurous and fearless nature is remembered through her research and impact on Lucy’s life.

A Rockport fisherman and high school friend of Helen and Tom, who becomes more involved with Lucy and Tom’s lives throughout the story.

Lucy and Tom’s elderly neighbor, viewed as a mentor figure and close friend to the Everhart family.

Helen’s former mentor, living in Maine, who shares stories and photographs of her with Lucy.

Fred’s older sister with artistic flair, who supports Lucy as she navigates the challenges of adolescence.

Fred and Fiona’s mother, who has faced her own struggles while raising her children alone.

A biologist who worked with Helen and continues her research, inspiring Lucy’s scientific curiosity.