“Avinguda Diagonal,” Langdon shouted. “Al oeste.” To the west.

Impossible to miss on any map of Barcelona, Avinguda Diagonal crossed the entire width of the city, from the ultramodern beachside skyscraper Diagonal ZeroZero to the ancient rose gardens of Parc de Cervantes—a ten-acre tribute to Spain’s most celebrated novelist, the author of Don Quixote.

The pilot nodded his confirmation and banked to the west, following the slanting avenue westward toward the mountains. “Address?” the pilot called back. “Coordinates?”

I don’t know the address, Langdon realized. “Fly to the fútbol stadium.”

“¿Fútbol?” He seemed surprised. “FC Barcelona?”

Langdon nodded, having no doubt the pilot knew exactly how to find the home of the famed Barcelona fútbol club, which was located a few miles farther up Avinguda Diagonal.

The pilot opened the throttle, now tracing the path of the avenue at full speed.

“Robert?” Ambra asked quietly. “Are you okay?” She studied him as if perhaps his head injury had impaired his judgment. “You said you know where to find Winston.”

“I do,” he replied. “That’s where I’m taking us.”

“A fútbol stadium? You think Edmond built a supercomputer at a stadium?”

Langdon shook his head. “No, the stadium is just an easy landmark for the pilot to locate. I’m interested in the building directly beside the stadium—the Gran Hotel Princesa Sofía.”

Ambra’s expression of confusion only deepened. “Robert, I’m not sure you’re making sense. There’s no way Edmond built Winston inside a luxury hotel. I think we should take you to the clinic after all.”

“I’m fine, Ambra. Trust me.”

“Then where are we going?”

“Where are we going?” Langdon stroked his chin playfully. “I believe that’s one of the important questions Edmond promised to answer tonight.”

Ambra’s expression settled somewhere between amused and exasperated.

“Sorry,” Langdon said. “Let me explain. Two years ago, I had lunch with Edmond at the private club on the eighteenth floor of the Gran Hotel Princesa Sofía.”

“And Edmond brought a supercomputer to lunch?” Ambra suggested with a laugh.

Langdon smiled. “Not quite. Edmond arrived for lunch on foot, telling me he ate at the club almost every day because the hotel was so convenient—only a couple of blocks from his computer lab. He also confided in me that he was working on an advanced synthetic intelligence project and was incredibly excited about its potential.”

Ambra looked suddenly heartened. “That must have been Winston!”

“My thoughts exactly.”

“And so Edmond took you to his lab!”

“No.”

“Did he tell you where it was?”

“Unfortunately, he kept that a secret.”

The concern rushed back into Ambra’s eyes.

“However,” Langdon said, “Winston secretly told us exactly where it is.”

Now Ambra looked confused. “No, he didn’t.”

“I assure you, he did,” Langdon said, smiling. “He actually told the whole world.”

Before Ambra could demand an explanation, the pilot announced, “¡Ahí está el estadio!” He pointed into the distance at Barcelona’s massive stadium.

That was fast, Langdon thought, glancing outside and tracing a line from the stadium to the nearby Gran Hotel Princesa Sofía—a skyscraper overlooking a broad plaza on Avinguda Diagonal. Langdon told the pilot to bypass the stadium and instead take them up high over the hotel.

Within seconds, the helicopter had climbed several hundred feet and was hovering above the hotel where Langdon and Edmond had gone to lunch two years ago. He told me his computer lab was only two blocks from here.

From their bird’s-eye vantage point, Langdon scanned the area around the hotel. The streets in this neighborhood were not as rectilinear as they were around Sagrada Família, and the city blocks formed all kinds of uneven and oblong shapes.

It has to be here.

With rising uncertainty, Langdon searched the blocks in all directions, trying to spot the unique shape that he could picture in his memory. Where is it?

It was not until he turned his gaze to the north, across the traffic circle at the Plaça de Pius XII, that Langdon felt a twinge of hope. “Over there!” he called to the pilot. “Please fly over that wooded area!”

The pilot tipped the nose of the chopper and moved diagonally one block to the northwest, now hovering over the forested expanse where Langdon had pointed. The woods were actually part of a massive walled estate.

“Robert,” Ambra shouted, sounding frustrated now. “What are you doing? This is the Royal Palace of Pedralbes! There is no way Edmond built Winston inside—”

“Not here! Over there!” Langdon pointed beyond the palace to the block directly behind it.

Ambra leaned forward, looking down intently at the source of Langdon’s excitement. The block behind the palace was formed by four well-lit streets, intersecting to create a square that was orientated north–south like a diamond. The diamond’s only flaw was that its lower-right border was awkwardly bent—skewed by an uneven jog in the line—leaving a crooked perimeter.

“Do you recognize that jagged line?” Langdon asked, pointing to the diamond’s skewed axis—a well-lit street perfectly delineated against the darkness of the wooded palace grounds. “Do you see the street with the little jog in it?”