“I couldn’t sleep for thinking about it… I suddenly realised that what I was analysing was the only possible move.” Munoz put his pocket chess set down on the table, smoothed out his original sketch, now crumpled and heavily annotated, and placed it beside the set. “Even then, I couldn’t believe it. It took me an hour to go over it all again, from start to finish.”

They were in an all-night bar-cum-supermarket, sitting by a large window that gave them a clear view of the broad, empty avenue. There was hardly anyone there, a few actors from a nearby theatre and half a dozen night birds, male and female. A security guard in paramilitary uniform was standing next to the electronic security gates at the entrance, yawning and looking at his watch.

“Now,” said the chess player, pointing first at the sketch and then at the small chessboard, “have a look at this. We managed to reconstruct the last move made by the black queen, from b2 to c2, but we didn’t know what the previous move by White was that forced her to do that… Remember? When we looked at the threat from the two white rooks, we decided that the rook on b5 could have come from any of the squares on 5; but that couldn’t explain why the black queen fled, since she would already be in check by another white rook, the one on b6. Maybe, we said, the rook had captured another black piece on b5. But which piece? That’s where we got stuck.”

“And which piece was it?” Julia was studying the board. Its geometrical black-and-white design was no longer unfamiliar, but one in which she could move about as if in familiar territory. “You said you could find out which it was by studying the pieces off the board.”

“And that’s what I did. I studied the pieces one by one, and I reached a surprising conclusion.

“Which piece could the rook on b5 have taken?” Munoz looked at the board with his insomniac eyes, as if he genuinely didn’t know the answer. “It wasn’t a black knight, since both are still on the board. It wasn’t the bishop either, because square b5 is white and the black bishop that can move along the white diagonal hasn’t as yet left its original position. It’s still there on c8 with its two escape routes blocked by pawns that have not yet come into play.”

“Perhaps it was a black pawn,” suggested Julia. Munoz shook his head.

“That took me longer to reject as a possibility, because the position of the pawns is the most confusing thing about this game. But it couldn’t have been any of the black pawns because the one on a5 came from c7. As you know, pawns capture by moving one square diagonally forwards, and that one presumably captured two white pieces on b6 and a5. As regards the other four black pawns, they were obviously miles away when they were captured. They would never have been anywhere near b5.”

“Then it must have been the black rook. The white rook must have taken it on b5.”

“No, that’s impossible. Given the arrangement of the pieces around a8, it’s obvious that the black rook was captured there, on its original square, without ever having moved. It was taken by a white knight -although in this case it doesn’t much matter which piece it was captured by.”

Julia looked up from the board, disoriented.

“I don’t get it. That discounts all the black pieces. Which piece did the white rook take on b5 then?”

Munoz gave a half-smile, which was not in the least bit smug; he merely seemed amused by Julia’s question, or perhaps by the answer he was about to give.

“The fact is it didn’t take any. Now don’t look at me like that. Your painter Van Huys was also a master when it came to laying false trails. It turns out that nothing was captured on square b5.” He crossed his arms and leaned over the small board, suddenly silent. Then he looked at Julia and laid one finger on the black queen. “If the last move by White wasn’t a threat to the black queen by the rook, that means that a white piece must have moved and thus discovered the check by the white rook on the black queen. I mean a white piece that was either on square b4 or b3. Van Huys must have had a good laugh, knowing that anyone trying to solve the riddle was bound to be fooled by that ruse with the two rooks.”

Julia nodded slowly. A few words from Munoz were all it took to make a corner of the board, apparently static and unimportant, suddenly fill with infinite possibilities. There was something truly magical about his ability to guide other people through the complex black-and-white labyrinth to which he possessed the hidden keys. It was as if he were able to orient himself by means of a network of connections flowing beneath the board and giving rise to impossible, unsuspected combinations which he had only to mention for them to come to life, to become so obvious that you were amazed not to have noticed them before.

“I see,” she said, after a few seconds. “That white piece was protecting the black queen from the rook. And, by moving away, it left the black queen in check.”

“Exactly.”

“And which piece was it?”

“Perhaps you can work it out for yourself.”

“A white pawn?”

“No. One was captured on a5 or b6 and the other one is too far away. It couldn’t have been any of the others either.”

“Well, frankly, I haven’t got a clue then.”

“Have a good look at the board. I could have told you right at the start, but that would deprive you of a pleasure which, I suppose, you deserve. Take your time.” He made a gesture encompassing the bar, the deserted street and the coffee cups on the table. “We’re in no hurry.”

Julia concentrated on the board. Soon, without taking her eyes off the game, she got out a cigarette, and a slight, indefinable smile appeared on her face.

“I think I may have got it,” she said cautiously.

“OK, what do you think?”

“The bishop that can move diagonally along the white squares is on fl, intact, and hasn’t had time to move there from his only possible original position, b3, since b4 is a black square.” She looked at Munoz for confirmation before going on. “I mean, it would have taken at least” – she counted with her finger on the board – “three moves to get from b3 to its present position. That means that it wasn’t a move by the bishop that left the black queen in check to the rook. Am I right?”

“Absolutely. Go on.”

“It couldn’t have been the white queen, now on el, that discovered the check either. Nor the white king. As for the white bishop that can move on the black squares, and is now off the board because it was taken, that could never have been on b3.”

“Very good,” said Munoz. “Why not?”

“Because b3 is a white square. Anyway, if that bishop had moved diagonally along the black squares from b4, it would still be there on the board, and it isn’t. I imagine it was taken some time before, during an earlier stage of the game.”

“Correct. So what are we left with then?”

Julia looked at the board and a slight shiver crept down her spine and down her arms, as if someone had just run the blade of a knife over her skin. There was only one piece they had not yet mentioned.

“The only piece left is the knight,” she said, swallowing hard, her voice involuntarily low. “The white knight.”

Munoz leaned towards her gravely.

“That’s right, the white knight.” He remained silent for a while, not looking at the board now but at Julia. “It was the white knight that moved from b4 to c2, thus uncovering the black queen and placing her in danger. And it was there, on c2, that the queen, in order both to protect herself from the rook and to gain another piece, took the knight.” Munoz fell silent again, checking that he hadn’t left out anything of importance. Then the gleam in his eyes went out, as abruptly as if someone had switched it off. He looked away from Julia as he picked up the pieces in one hand and folded the board with the other, apparently signalling the end of his intervention in the matter.