The narrator, Ellie Cruz, turns 12 during the story. She lives with her mom, Lissa, attends a local middle school, and becomes close to her grandfather, Melvin, a scientist. At first, living in a small, cramped house, she misses her absent best friend and must come to terms with her cranky grandpa. Ellie loves puzzles and is methodical in her activities; her personality is well suited to scientific research, and her grandfather takes her under his wing and inspires her with stories about the great researchers.

Ellie realizes she must say goodbye to her childhood and its friendships and begin to look forward to the possibility of life as a budding scientist; she also makes new friends. She realizes that, even for scientists, there’s more to life than the relentless pursuit of glory.

Melvin Herbert Sagarsky, PhD, is Ellie’s brilliant-but-grumpy grandfather. He’s also a researcher who discovers a cure for aging. The cure returns him to the physical age of a teenager. Despite his achievements, Melvin struggles with feeling out of step in a changing world. He wishes things would return to a time when he was more appreciated. His old-fashioned clothes, long hair, inability to enter his science lab, anonymity as an old genius in a teenage body, and lack of respect from the scientific community all conspire to keep him from the fame and honor to which he believes he’s entitled.