Thinking afterwards of his wonderful old maniac of a friend, Dyer said to himself that he would be entitled to believe their whole afternoon together had been a dream. If he had been in the Andes, climbing Mount Ausangate, he would be asking himself if he had seen Rougetel, or was it the altitude?

‘Has he changed?’ Leandro wanted to know.

In spite of everything that had happened in between, some vital part of him had remained untouched. He still wanted to get to the nub.

‘I’d say hardly at all.’

Chapter Forty

‘A TROUT FLY CAN’T BE withdrawn the way it has entered,’ said his father. ‘It must be pushed right through.’

So with Marvar’s post-it note. Dyer could not rebury it in the sandpit, he couldn’t leave it folded in limbo inside a library book. He had to pull it up, out, away.

Next morning, Dyer resolved to finish what his encounter with Rougetel had interrupted. To avoid arousing any further suspicion, he had had to persuade himself that his solution lay in plucking out Marvar’s algorithm and destroying it. The sooner he accomplished this the better; no one must know it had existed. He no longer saw it in terms of the gains or dangers to humanity, only its impact on him. It had to be destroyed so that he did not die, and so that he and Leandro could live. He wasn’t brave. He wanted to be safe and his son to be safe. Simple.

From near the bottom of his reserved pile, Dyer prised loose the calf-bound volume and took it next door. As soon as he opened the back cover and his eyes fell on the folded piece of paper floating around the map of Brazil, he felt the tension subside that had been growing as he climbed the staircase.

He lifted his eyes to the wall opposite, and his obliterating impulse receded, and he was overtaken by a warm, inexplicable calm, as if a blue haze has enveloped him.

He is back in the Café Lisboa. Rougetel is riffling through the book he has produced from his rucksack. Its pages flutter like a kaleidoscope of butterflies with yellow post-it notes to mark the passages which had captivated him.

Even as Dyer detaches Marvar’s note, Rougetel’s voice is knocking on his thoughts.

It’s almost the last thing Rougetel says to him. They’re standing at the school gate, Rougetel is talking about how close he is to wrapping up his research into the human brain, and looking forward to immersing himself in something quite new, although he has yet to decide what this will be.