Don is the protagonist and first-person narrator throughout the book. He is around 40, born and raised in Australia, and was a professor of genetics at Melbourne University before taking a research position at Columbia. Don’s mother, father, and brother, Trevor, live in his hometown in Australia. His sister died a few years prior of an undiagnosed ectopic pregnancy, which provides background to Don’s anxieties about Rosie’s health during pregnancy and adds to his subconscious motivation to monitor her nutrition, exercise, and alcohol intake.

Don is methodical, but adapts his comfort level and routine for Rosie. For example, though he normally avoids physical contact with others, he enjoys contact with Rosie. Don’s habit of creating lists becomes a narrative device that adds humor to the novel and showcases his problem-solving abilities.

He is also skilled at memorizing, which makes him proficient in scientific fields, martial arts, and cocktails. Though he struggles with understanding others’ emotions, he is an astute observer and loyal friend. Don’s traits are indicative of Autism Spectrum Disorder (ASD), but he simply thinks of himself as “wired” differently.

Don’s struggles with the fear that he will be an inadequate father due to his lack of facility with emotion.