“Of course that’s the argument scientists use in its favour.” She stopped herself. One step at a time, she thought. “Do you know what genetic engineering is?”

He shrugged, reluctant to admit his ignorance. “I suppose not.”

“And do you know why you don’t?” He didn’t. “Because a lot of scientists think that we laymen are too stupid to understand it. In fact it’s really very simple. But they don’t want to explain, because if we understood it we might just be scared of it.”

He glanced at her across the Jeep. “You seem to know a lot about it.”

“Oh yes,” she said bitterly. “I lived with it for nearly seven years.” And she remembered Michael’s earnest passion which she had shared, infected by his commitment and enthusiasm. It was strange, she thought now, how that passion lived on in her still, while all feeling for Michael had withered and died.

He recognised the same bitterness he had seen in her at the Sichuan restaurant, and it came back to him that she had told him her husband lectured in genetics. He knew that somehow he had touched on the same raw nerve, then and now. “So explain it to me,” he said.

“You know what DNA is?”

“Sort of.”

“It’s just a code. A sequence of genes that determines the nature of all living things—their substance, their characteristics. So, suppose you grow tomatoes, and all your tomatoes are being destroyed by a certain type of caterpillar. What do you do?”

“I don’t know. Spray them with an insecticide, I guess, to kill the caterpillar.”

“That’s what people have been doing for years. Trouble is, it contaminates the food, it contaminates the environment, and it costs a lot of money. But now you discover that a certain type of potato you are growing is never attacked by these caterpillars. In fact, they positively avoid it. And you find out that the reason for this is that the potato, in its genetic code, has a gene that creates a substance that is poisonous to the caterpillar. So, says your friendly neighbourhood genetic engineer, here’s the solution to your tomato problem. You take the gene that creates the poison in the potato and insert it into the DNA of the tomato. And, bingo, suddenly you’ve got a tomato that the caterpillars will avoid like the plague.”

“It sounds like a pretty good idea.”