“It was painted in what is now Belgium,” Cesar said, “around 1470.”

“I don’t think there’ll be any problem then. Nothing insoluble at any rate.”

Julia got up from the table and went over to the painting to look at the position of the painted chess pieces.

“How do you know that Black has just moved?”

“It’s obvious. You just have to look at the position of the pieces. Or at the players.” Munoz pointed to Ferdinand of Ostenburg. “The one on the left, the one playing Black and looking towards the painter, or towards us, is more relaxed, even distracted, as if his attention were directed at the spectators rather than at the board.” He pointed to Roger de Arras. “The other man, however, is studying a move his opponent has just made. Can’t you see the concentration on his face?” He returned to his sketch. “There’s another way of checking it; in fact, it’s the method to use. It’s called retrograde analysis.”

“What kind of analysis?”

“Retrograde. It involves taking a certain position on the board as your starting point and then reconstructing the game backwards in order to work out how it got to that position. A sort of chess in reverse, if you like. It’s all done by induction. You begin with the end result and work backwards to the causes.”

“Like Sherlock Holmes,” remarked Cesar, visibly interested.

“Something like that.”

Julia had turned towards Munoz, impressed. Until now, chess had been only a game for her, a game with rules marginally more complex than those for Parcheesi or dominoes and requiring greater concentration and intelligence. But from Munoz’s reaction to the Van Huys it was evident that the planes represented in the painting: mirror, room, window – the backdrop to the moment recorded there by Pieter Van Huys, a space in which she herself had experienced the dizzying effects of the optical illusion created by the artist’s skill – presented no difficulties at all for Munoz, who knew almost nothing about the picture and hardly anything about its disquieting connotations. For him, it was a familiar space beyond time and personalities. It was a space in which he appeared to move easily, as if, by making everything else an abstraction, he was able at once to take in the position of the pieces and integrate himself into the game. The more he concentrated on The Game of Chess, the more he shed the perplexity, reticence and awkwardness he’d shown in the bar, and revealed himself as the confident, impassive player she had thought him to be when she saw him at the Capablanca Club. It was as if this shy, grey, hesitant man needed only the presence of a chessboard to recover his confidence and self-assurance.

“You mean it’s possible to play the game of chess in the painting backwards, right back to the beginning?”

Munoz made one of his noncommittal gestures.

“I don’t know about going right back to the beginning… but I imagine we could reconstruct a fair number of moves.” He looked at the painting again as if he’d just seen it in a new light and, addressing Cesar, he said: “I suppose that was exactly what the painter intended.”

“That’s what you have to find out,” replied Cesar. “The tricky question is: Who took the knight?”

“You mean the white knight,” said Munoz. “There’s only one left on the board.”

“Elementary,” said Cesar, adding with a smile, “my dear Watson.”

Munoz ignored this; humour was evidently not one of his strong points. Julia went over to the sofa and sat down next to Cesar, as enthralled as a little girl watching some thrilling performance. Munoz had finished his sketch now and he showed it to them.

“This,” he explained, “is the position of the pieces as they are in the painting.”

“As you see, I’ve given each square a coordinate, to make locating the pieces easier for you. So, seen from the perspective of the player on the right…”

“Roger de Arras,” said Julia.

“Yes, Roger de Arras. Looking at the board from that position, we number the squares on the vertical from one to eight and assign a letter, from a to h, to each of the squares on the horizontal,” he said, pointing to them with his pencil. “There are other more technical classifications, but that might just confuse you.”

“And each symbol corresponds to a chess piece?”

“That’s right. They’re conventional symbols, some black, some white. I’ve made a note, below, of what each one means.”

“That way, even if you know very little about chess, it’s easy to see that the black king, for example, is on square a4, and that on fl, for example, there’s a white bishop. Do you understand?”

“Perfectly.”

Munoz went on to show them some further symbols he’d drawn.

“Now, we’ve looked at the pieces actually on the board, but in order to analyse the game, it’s essential to know which ones are off the board too, the pieces that have already been taken.” He looked at the picture. “What’s the player on the left called?”

“Ferdinand of Ostenburg.”

“Well, Ferdinand of Ostenburg, who’s playing Black, has taken the following white pieces.”

“That is: a bishop, a knight and two pawns. For his part, Roger de Arras has taken the following pieces from his rival.”

“That’s four pawns, one rook and a bishop.” Munoz looked thoughtfully at the sketch. “When you look at the game from that point of view, White would seem to have an advantage over his opponent. But, if I’ve understood correctly, that’s not the problem. The question is who took the white knight. Clearly it must have been one of the black pieces, which may seem to be stating the obvious, but we have to go step by step here, right from the beginning.” He looked at Cesar and Julia as if what he’d said required some apology. “There’s nothing more misleading than an obvious fact. That’s a principle from logic which is equally applicable in chess: what seems obvious doesn’t always turn out to be what really happened or what is about to happen. To sum up: this means that we have to find out which of the black pieces on or off the board took the white knight.”

“Or killed him,” added Julia.

Munoz made an evasive gesture.

“That’s not my business, Senorita.”

“You can call me Julia, if you like.”

“Well, Julia, it’s still not my business.” He looked hard at the paper containing the sketch as if written on it was the script of a conversation of which he’d lost the thread. “I believe you brought me here to tell you which chess piece took the white knight. If by finding that out, the two of you are able to draw certain conclusions or decipher some hieroglyph, that’s fine.” He looked at them with more assurance, as often happened when he’d concluded a technical exegesis, as if he drew some measure of confidence from his knowledge. “That’s up to you. I’m just a chess player.”

Cesar found this reasonable.

“I can’t see anything wrong with that,” he said, looking at Julia. “He makes the moves and we interpret them. Teamwork, my dear.”

Julia was too interested in the whole problem to bother with details about method. She put her hand on Cesar’s, feeling the soft, regular beat of his pulse beneath the skin on his wrist.

“How long will it take to solve?”

Munoz scratched his ill-shaven chin.

“I don’t know. Half an hour, a week. It depends.”

“On what?”

“On a lot of things. On how well I manage to concentrate. And on luck.”

“Can you start right now?”

“Of course. I already have.”

“Go on then.”

But at that moment the phone rang, and the game of chess had to be postponed.