Trying to ignore him, Jack stood and pulled at his own shackles. While he had every faith in Akiko, there was a good chance she would not find the keys to his irons. So rather than sitting around and doing nothing, he yanked on the chains again. But the bolts held firm.

‘Go on!’ encouraged Mad Bob. ‘Haul away, me hearty. I’d like to see ye trying to drag a whole prison wall with ye!’

Putting a foot against the brickwork and gritting his teeth, Jack wrenched hard. He jerked and tugged until his strength gave out and he collapsed on the floor, breathless, his heart pounding.

‘I think it moved at least half an inch,’ said Mad Bob earnestly.

Jack glared at him, then began trying to pull his hands out through the iron cuffs. But the shackles were far too tight and his efforts only resulted in scraping skin and bloodying his wrists.

‘Oh, that looks like it hurts,’ sympathized the inmate. ‘But give it another few months and they’ll slip right through –’

‘Shut up, Bob!’ snapped Jack, his patience worn thin. Just then, he heard a trickle of water and turned round. Yori stood in the corner of his cell, urinating.

‘There’s a bucket for that, don’t you know!’ said Mad Bob indignantly, as if such conduct was inappropriate in their already squalid surroundings.

Yet even Jack was surprised. Such ill manners were totally out of keeping with his Japanese friend’s behaviour. ‘What are you doing?’ he demanded.

‘Back-up plan,’ Yori replied, now getting on his hands and knees and scraping away at the wall with the edge of one of his metal cuffs. ‘The brickwork is eroded from frost and damp. My piss should help dissolve the crumbling mortar, and with a bit of extra encouragement –’ he gouged out a lump of mortar, then worked away at the wall – ‘there!’

Yori pulled out a brick. A back alley – and freedom – was visible through the narrow hole.

‘Good work, Yori!’ said Jack as another brick came loose, then another.

Mad Bob began tutting in disapproval. ‘Julius won’t be happy with that!’ he remarked.

As Yori widened the hole, they heard the jangle of keys and footsteps descending the stairwell. Jack exchanged a hopeful look with Yori. When Akiko returned with the keys, they’d all be free.

‘Don’t know what you two are smiling about,’ said Mad Bob. ‘That ain’t your friend coming back. That’s Julius!’

And, as their fellow inmate began to cackle crazily, Jack realized he was right. The footsteps were too heavy to be Akiko’s.

‘Go!’ Jack hissed to Yori. ‘Get out while you can.’

Yori’s eyes widened in horror. ‘But what about you?’

‘I’ll be fine,’ said Jack as lamplight spilled from the stairwell into the prison block. ‘Now go!’