Alberti. Paul pointed to a small volume on the far shelf. The spine read De re aedificatoria. That's what Colonna meant by it. He was about to borrow an idea from Alberti's book, and he wanted you to notice it. If you could just figure out what it was, the rest would fall into place.

In his treatise, Alberti creates Latin equivalents for architectural words derived from Greek. Francesco does the same replacement all over the Hypnerotomachia—except in one place. I'd noticed it the first time I translated the section, because I started hitting Vitruvian terms I hadn't seen in a long time. But I never thought they were significant.

The trick, I realized, was that you had to find all the Greek architectural terms in that passage and replace them with their Latin equivalents, the same way they appear in the rest of the text. If you did that, and used the acrostic rule-reading the first letter of each word in a row, the same way you do with the first letter of each chapter-the puzzle unlocks. You find a message in Latin. The only problem is, if you make just one mistake converting the Greek to Latin, the whole message breaks down. Replace entasi with ventris diametrum instead of just venter, and the extra 'D' at the beginning of diametrum changes everything.

He flipped to another page, talking faster. I made mistakes, of course. Luckily, they weren't so big that I couldn't still piece together the Latin. I took me three weeks, right up to the day before you guys came back to campus. But I finally figured it out. You know what it says? He scratched nervously at something on his face. It says: Who cuckolded Moses?

He gave a hollow laugh. I swear to God, I can hear Francesco laughing at me. I feel like the whole book just boiled down to one big joke at my expense. I mean, seriously. Who cuckolded Moses?

I don't get it.

In other words, who cheated on Moses?

I know what a cuckold is.

Actually, it doesn't literally say cuckold. It says, 'Who gave Moses the horns?' Horns, as early as Artemidorus, are used to suggest cuckoldry. It comes from-

But what does that have to do with the Hypnerotomachia?

I waited for him to explain, or to say that he'd read the riddle wrong. But when Paul got up and started pacing, I could tell this was more complicated.

I don't know. I can't figure out how it fits with the rest of the book. But here's the strange thing. I think I may have solved the riddle.

Someone cuckolded Moses?

Well, sort of. At first, I thought it had to be a mistake. Moses is too major a figure in the Old Testament to be associated with infidelity. As far as I knew, he had a wife-a Midianite woman named Zipporah-but she barely appeared in Exodus, and I couldn't find any reference to her cheating on him.

Then in Numbers 12:1, something unusual happens. Moses' brother and sister speak against him because he marries a Cushite woman. The details are never explained, but some scholars argue that because Cush and Midian are completely different geographical areas, Moses must've had two wives. The name of the Cushite wife never appears in the Bible, but a first-century historian, Flavius Josephus, writes his own account of Moses' life, and claims that the name of the Cushite, or Ethiopian, woman he married was Tharbis.

The details were beginning to overwhelm me. So she cheated on him?

Paul shook his head. No. By taking a second wife, Moses cheated on her, or on Zipporah, whichever one he married first. The chronology is hard to figure out, but in some usages, cuckold's horns appear on the head of the cheater, not just the cheater's spouse. That must be what the riddle's getting at. The answer is Zipporah or Tharbis.

So what do you do with that?

His excitement seemed to dissipate. That's where I've hit a wall. I tried to use Zipporah and Tharbis as solutions every way I could think of, applying them as ciphers to help crack the rest of the book. But nothing works.

He waited, as if expecting me to contribute something.

What does Tart think about it? was all I could think to ask.

Vincent doesn't know. He thinks I'm wasting my time. As soon as he decided Gelbman's techniques weren't yielding breakthroughs, he told me I should go back to following his lead. More focus on the primary Venetian sources.

You're not going to tell him about this?

Paul looked at me as if I misunderstood.

I'm telling you, he said.

I have no idea.

Tom, it can't be an accident. Not something this big. This is what your father was looking for. All we have to do is figure it out. I want your help.

Why?

Now a curious certainty entered his voice, as if he understood something about the Hypnerotomachia that he'd overlooked before. The book rewards different kinds of thought. Sometimes patience works, attention to detail. But other times it takes instinct and inventiveness. I've read some of your conclusions on Frankenstein. They're good. They're original. And you didn't even break a sweat. Just think about it. Think about the riddle. Maybe you'll come up with something else. That's all I'm asking.

There was a simple reason why I rejected Paul's offer that night. In the landscape of my childhood, Colonna's book was a deserted mansion on a hill, a foreboding shadow over any nearby thought. Every unpleasant mystery of my youth seemed to trace its origins to those same unreadable pages: the unaccountable absence of my father from our dinner table so many nights as he labored at his desk; the old arguments he and my mother lapsed into, like saints falling into sin; even the inhospitable oddness of Richard Curry, who fell for Colonna's book worse than any man, and never seemed to recover. I couldn't understand the power the Hypnerotomachia exerted over everyone who read it, but in my experience that power always seemed to play out for the worse. Watching Paul struggle for three years, even if it culminated in this breakthrough, had only helped me keep my distance.

If it seems surprising, then, that I changed my mind the next morning, and joined Paul in his work, chalk it up to a dream I had the night after he told me about the riddle. There is a woodcut in the Hypnerotomachia that will always stay in the stowage of my early childhood, a print that I bumped into many times after sneaking into my father's office to investigate what

he was studying. It's not every day that a boy sees a naked woman reclining under a tree, looking up at him as he returns the favor. And I imagine no one, outside the circle of Hypnerotomachia scholars, can say he has ever seen a naked satyr standing at the feet of such a woman, with a horn of a penis extended like a compass needle in her direction. I was twelve when I saw that picture for the first time, all alone in my father's office, and I could suddenly imagine why he sometimes came to dinner late. Whatever this was, strange and wonderful, beef potluck had nothing on it.

It returned to me that night, the woodcut of my childhood-woman lounging, satyr stalking, member rampant-and I must have done a lot of turning in my bunk, because Paul looked down from his and asked, You okay, Tom?

Coming to, I rose and shot through the books on his desk. That penis, that misplaced horn, reminded me of something. There was a connection to be made. Colonna knew what he was talking about. Someone had given Moses horns.

I found the answer in Hartt's History of Renaissance Art. I'd seen the picture before, but never made anything of it.

What are these? I asked Paul, tossing the book up to his bunk, pointing at the page.

He squinted. Michelangelo's statue of Moses, he said, staring at me as if I'd lost my mind. What's wrong, Tom?