I had to think for a minute before I understood the last sentence.

“I think I see,” I said, finally.

“It took me a while,” my father said, “but when I understood, I felt comfort beyond measure. I had a sense that I’d always known these truths, but only when I heard the words did they begin to guide my actions.

“The next time that Malcolm came by, I told him I’d have no more of his cannibalistic nonsense. With Dennis’s help, I was strong enough to return to my studies and to live with my affliction.”

“Malcolm left you alone?”

“Eventually, he did. At first he tried to argue otherwise. He said that my place was in his lab, since he’d given me a chance to live forever.

“But vampirism is no guarantee of eternal life. Contrary to the Internet lore you’ve brought me, only a small percentage of those who’ve changed states lives more than a hundred years. Many get themselves killed through their own acts of aggression or arrogance. They die as painfully as mortals do.”

“Surely there are compensations?”

My father had clasped his hands beneath his chin, and he gazed at me with an expression as close to love as I’d ever seen in his eyes. “Yes, Ari,” he said, his voice soft. “As I said before, there are compensations.”

My father paused to answer a knock on the door. Someone, probably Root, handed him a silver tray with two glasses of Picardo on it. He shut the door and carried the tray to me. “Take the glass on the left,” he said.

Another first, I thought, taking the glass. My father set down the tray. He took the other glass and raised it in a toast: “Gaudeamus igitur / iuvenes dum sumus.”

“So let us rejoice / While we are young,” I translated. “I’ll have that inscribed on my tombstone.”

“Mine as well.” It was our first shared joke. We clinked the glasses and drank.

The stuff tasted awful, and I guess my face showed that. My father almost laughed. “Another taste to be acquired,” he said.

“Or not,” I said. “What’s in this stuff?”

He held the glass up and swirled the red liquid. “It’s an aperitif. From the Latin aperire.”

“To open,” I said.

“Yes, to open the taste buds before a meal. The first aperitifs were made from herbs and spices, and the roots and fruit of plants.”

“What makes it so red?”

My father set down his glass. “The recipe is a secret, created and kept by the Picardo family.”

As we sipped our cocktails, my father resumed his story. Those who undergo the “change of state,” as my father calls it, immediately are aware of their new nature. But when a vampire and a mortal beget a child, that child’s nature is indeterminate.

“I’ve read atrocious accounts of parents exposing a half-breed child to sunlight — using ropes and stakes to tie it down, then leaving it to see if it burned,” he said. “But photosensitivity isn’t a certain sign of vampirism. Even in the general population, sensitivity to sun can fluctuate widely.”

I wasn’t sure I liked the term half-breed.

“I used the historical term,” my father said. “Today, we prefer to use the term diverse.”

I took a small sip of Picardo and forced myself to swallow it without tasting it.

“Isn’t there a blood test for vampirism?” I asked.

“Not a reliable one.” He crossed his arms across his chest, and I found myself noticing the muscles in his neck.

My father told me that vampires exist everywhere, in every country and in every profession. Not surprisingly, many of them are drawn to scientific research, particularly areas involving blood, but others serve as teachers, lawyers, farmers, and politicians. He said that two current U.S. congressmen reportedly were vampires; according to Internet rumors, one of them was thinking about “coming out of the box” — a euphemism for publicly acknowledging one’s vampire nature.

“I doubt he’ll do it anytime soon,” my father said. “Americans aren’t ready to accept vampires as normal citizens. All they know are the myths propagated by fiction and films.” He picked up my journal and set it down again. “And the Internet.”

I took a deep breath. “What about the mirrors?” I said. “And the photographs?”

“I wondered when you’d ask that question.” He gestured toward the shadowbox on the wall and beckoned me.

We both stood before the picture. For a moment I didn’t understand the point. Then I saw a faint reflection of myself in the domed glass. There was no reflection of my father. I turned to make sure he was still next to me.

“It’s a protective mechanism,” he said. “We call it emutation. Vampires emutate to varying extents. We can make ourselves entirely invisible to humans or produce a blurred or partial image by controlling our bodies’ electrons, keeping them from absorbing light. It’s a voluntary action that becomes so instinctive that it seems involuntary, over time. When your friend tried to snap my picture, my electrons shut down and let the light in the room — the electromagnetic radiation, to be more precise — pass through me.”

I thought for half a minute. “Why didn’t the photo show your clothes? And why aren’t they in the mirror?”

“My clothing and shoes are made from ‘metamaterials,’” he said. “The fabrics are based on metals, because metals respond so well to light; that’s why they’re used to make mirrors. When my body’s electrons shut off, my skin temperature elevates, and the materials’ microscopic structure is altered, allowing them to warp light, make it flow around me. So, when electromagnetic waves hit my clothing, they produce neither a reflection nor a shadow.”

“Cool.” I said it without thinking.

“Some British tailors are wizards,” he said. “In any case, invisibility is one of the compensations that come with the affliction, if you want to call it that. Along with access to the world’s best tailors.”

“Do you call it an affliction?” I looked at the place in the glass where my father’s reflection should have been.

He let me look for a few seconds more, then returned to his chair. “Hematophagy is only one aspect,” he said. “Our condition, if you will, has more to do with physics — with energy conversion, with changes in molecules’ temperatures and pressure patterns and movements. We need mammals’ blood, or good substitutes, in order to endure. We can subsist on relatively small amounts — something I’ve learned through personal experience and experiment — but we become weak unless we’re fed.”

I nodded. I was hungry.

As I tried to eat dinner (my first attempt at making vegetarian lasagna produced uninspiring results), my father sipped another cocktail and told me about the brighter side of vampirism.

“Before my change of state, I took so much for granted that now seems extraordinary,” he said. “My senses became a hundred times more acute. Malcolm advised me to take the world in small doses, to avoid being overwhelmed by it. Our new state of sensory awareness was similar, he said, to that induced by LSD.”

I set down my fork. “Did you ever take LSD?”

“No,” my father said. “But Malcolm described his own experience of it and said he found it comparable. He said ordinary experiences now took on new appearances and meanings. A walk through King’s College chapel while the organ was playing was almost too much for his senses to absorb. Colors became brilliant, sounds intensely true and pure, and all of the senses intermingled, so that he could simultaneously taste the texture of the stone walls, feel the smells of incense, see the sound of the carillon.”

“I can do that,” I said.

“Yes, I remember you telling me once that Wednesdays were always silver, while Tuesdays were lavender.”

As he spoke, I admired his shirt, which managed to be three colors — blue, green, and black — and no color at all.

“I also became sensitive to patterns,” he said. “Malcolm said not all of us share this trait. Certain designs — paisley, for instance, or the complicated patterns of Oriental carpets — are able to mesmerize me, unless I turn away. Needless complexity — complexity for no reason — arrests my attention, makes me look for the aberration that isn’t there. Apparently it’s related to my difficulty in opening things; it’s a form of dyslexia. Have you experienced it?”

“No.” For the first time I understood why none of the fabrics in the house was patterned, and why all of the doorknobs were oversized. “What about shape-shifting?”

“Another myth. I can become invisible, as I told you. I can hear others’ thoughts — not always, but usually. And I can” — he paused and made a dismissive gesture with his hands — “I can hypnotize others. But so can you, and so can many humans. It’s been said that Freud could control his family at the dinner table by the movement of his left eyebrow.”

“Was Freud one of us?”

“Good heavens, no,” my father said. “Freud was the father of psychoanalysis. No self-respecting vampire would have anything to do with that.”

I looked up from my food and saw a glint of humor in his eyes.

“All in all, these qualities aren’t what I consider assets, but rather unusual abilities that I choose to deploy as little as possible. The real assets are the obvious ones — never aging and enjoying potentially infinite longevity, immunity to many diseases and perils, and rapid recovery from limited exposure to the few to which we’re vulnerable.”

I pushed away my plate. “What are the few?”

“Erythema solare — that’s sunburn,” he said. “Fire. Severe heart injury.”

“Father,” I said, “am I mortal or not?”

“Part of you is, of course.” He curled one hand around the base of his cocktail glass. His hands were strong, but not square, with long fingers. “We simply don’t know yet how much. Matters will sort themselves out, as you age. Heredity is more than DNA, you know. Traits are also transmitted through behavior and symbolic communication, including language.”

“As I age,” I repeated. “Doesn’t that mean I am mortal — the fact that each year I’m different, while you remain the same?”

He set down his glass. “So far, yes, you are aging as mortals do. There may come a time when you choose” — he stopped talking for a moment, his face falling into familiar lines of sadness, but his eyes close to despair — “when you choose, or the choice is made for you, to stop aging.”

“I can choose?” This was something I hadn’t considered. “You can choose.” He looked again at my plate and grimaced.

“Your food is growing cold, with all these questions.”

I didn’t take the hint. “I have so many more to ask,” I said. “How do I go about choosing? And what happened to my mother? Is she dead?”

He put up his hand. “Too many questions. I’ll address them, but not in a piecemeal fashion. Let me tell you how it was between us, yes? And then, as I’ve said before, you’ll be able to answer the big questions yourself.”

I picked up my fork. He resumed his story.