“Your father,” D.D. stated once again, for the sake of argument.

Adeline’s expression never changed. “Given that I suffer from a rare genetic condition, no one knows the potential pitfalls of DNA better than I.”

D.D. found this intriguing. She leaned forward. “Did Harry have your same condition—is it possible he also couldn’t feel pain?”

“No. Congenital insensitivity to pain is caused by a double-recessive gene—meaning both parents must be carriers of the genetic mutation. Not to mention there are fewer than fifty cases known in the entire US, and half of the children diagnosed die before age three from heatstroke. Someone like me, grown to adulthood, with four fully functional limbs . . . I’m the exception, not the norm.”

“Why is that?”

“As part of the gene mutation, we can’t feel heat. Meaning we don’t sweat. For infants and toddlers, this is particularly dangerous. On a warm summer afternoon, their bodies can overheat to critical levels without them ever showing signs of distress. By the time the parents rush their listless baby to the hospital, it’s too late.”

D.D. couldn’t help herself. “So what do you during the summer?”

“Enjoy air-conditioning. Drink plenty of fluids. And I take my temperature multiple times a day. I can’t trust what I feel, Detective, which means I must rely on external diagnostics to tell me if my body is all right.”

“Melvin is useful,” D.D. murmured.

“Melvin is useful. I’ve never lain on a beach or walked in the full summer sun. I don’t even enter a shower without first checking the thermometer. And as for most athletic hobbies or fitness programs . . . It would be dangerous for someone like me to run or swim or play tennis or shoot hoops. I could blow out a knee, break an ankle, strain a shoulder and never be any the wiser. My health remains a matter of constant vigilance.”

D.D. nodded. She thought the good doctor spoke very matter-of-factly when describing a lifestyle that must actually feel very limiting and isolating. Forget never being picked for someone’s team in grade school; Adeline must have had to sit out the entire recess. Let alone never having the chance to walk hand in hand with a special someone on a sunny day. Or run hard and strong just because she felt like it. Or leap from point A to point B simply to see if she could make it.

A serious adult who no doubt grew up as a serious child, practicing constant vigilance. And realizing at a very young age that her rare condition inevitably set her apart, an outsider looking in.

Because Melvin wasn’t just useful. Melvin was common, pain being the great equalizer that brought everyone together.

“And your sister?” D.D. asked.

“She doesn’t share my condition.”

“So your adoptive father didn’t take her in.”

“No.”

“Must’ve pissed her off.”