Boole looked across the floor of the cave towards the two exits, each with its grim-looking guard, each of them gripping a Kalashnikov.

How was he going to get out of this?

Bloomfield’s gloating face was back in his head now, saying, ‘A pity, Mr Boole, that we may never meet again. Such an audacious adversary. Bold, daring and so terribly charming, especially without your Walther PPK. But, despite the threat you pose to my plans to reduce Tehran to rubble, for which the British and the Americans will get the blame, I’ve decided to give you a chance.’

‘How very sporting of you,’ Boole had said, feeling his senses slipping away again and seeing, fleetingly, the beguiling face of Tiffany Shagwell as she passed him the glass of Krug that he might have guessed contained more than just bubbles. He had to hold on. It was not usually Bloomfield’s way to throw a chap a lifeline, but if that was what the bastard was doing, good note had best be taken.

Bloomfield’s scar across his cheek had twitched and danced in sheer delight at the conundrum as he pointed to the other side of the cave. ‘Look, Mr Boole, two exits, two guards. One exit leads back to me that we may fight again, that you may thwart my scheme. The other leads to perdition. Certain death. Observe the guards now. Identical twins in all respects save one. They both know which exit you need, but one of them only tells lies, the other only the truth. But which is which, Mr Boole? You have one question, one question only, and you may ask it of only one guard. Break these rules and you will be gunned down like the dog that you are. What, Mr Boole, will that question be?’

And the face had fuzzed over then, faded to black, as Boole passed back into unconsciousness.

But Boole was awake now, wide awake, trying to calculate just how long he’d been lying here on this filthy floor, and how much time before Bloomfield tricked the Israelis into launching their strike and the conflagration that would surely follow. Bloomfield’s final throw of the dice. It seemed that this time he wanted destruction, pure and simple. The end of everything. And why should Bloomfield die and not take the whole world down with him?

Boole got to his feet, brushed himself down. Walking now towards the two exits, he saw there was a line drawn in the sandy soil. He guessed that this was where he should stop, ask the question; they would not want the risk of his getting too close. Sure enough, the guard on the right raised his gun and said, ‘No further, Mr Boole. What is your question and do you wish to ask me or my brother?’

Boole hesitated. Was this literally the end of the line? To be gunned down in this foul place, which would remind him of hell if it wasn’t so cold, or escape by solving the puzzle? One question. One guard. One exit. But what question and which guard should he ask? How could he determine who lied and who told the truth and at the same time be told which was the right way to go? But, he thought now, a tinsel-winged sliver of hope glimmering at the back of his mind, did he really need to know who the liar was ...?

Answers on a post card please to the usual address.