He went to a large steel cupboard and opened it. There were bits and pieces of equipment arranged along the shelves inside. He found what he was looking for and brought it out, closing the door again. It was a small black box, the size of one of Nick Christopher’s crossword dictionaries. Built into its top surface was what looked like an old-fashioned LED pocket calculator.

‘It was difficult,’ Izzard said proudly, ‘until I made this.’ He handed Hepton the box. Hepton examined it, but without success. The several home-made switches and push-buttons were unmarked.

‘I give up,’ he said. ‘What is it?’

‘It’s another number-cruncher of sorts,’ Izzard explained, pleased that Hepton hadn’t known. ‘Some of the companies use long numerical codes, and those were the worst to crack. All I needed to do was plug this box into my modem and it did all the work for me.’

‘Ingenious,’ said Hepton, examining the box more carefully.

‘No,’ said Izzard, ‘what’s really ingenious is that I cooked up a chip that put the other computer on hold while my computer was pumping the code numbers into it.’

Hepton saw the implications at once. ‘So you didn’t need to sign off and try again every time you got the code wrong?’

Izzard nodded his head vigorously, then gave a childish, high-pitched laugh.

‘Brilliant,’ said Hepton. ‘I hope you took out a patent on it.’

‘No,’ said Izzard, calming a little. ‘But I sold the idea to the military for fifteen thousand pounds.’ He lifted the black box out of Hepton’s hand and returned it to its cupboard. ‘God knows what they wanted it for,’ he said with finality.

As he closed the cupboard, a buzzer sounded. ‘That’ll be our spy,’ said Izzard, ‘wishing to come into the cold.’ He pressed a button on the wall, and the door clicked open again, admitting Sanders.

‘Cheery lot, those cab drivers,’ Sanders said grumpily. He was carrying a cardboard box. Hepton could smell the waft of fried sausage coming from within it, and realised he was hungry.

Izzard seemed to know what he was thinking. ‘Never work on an empty tum,’ he said, making for the box.

As the work continued, becoming ever more painstaking, Sanders fell asleep perched on a stool, his head and arms resting on a bench top. Izzard, however, seemed to grow more awake as the night progressed, while Hepton, though not feeling tired, began to feel disoriented, even hallucinatory for a few strange minutes.