And think. Every minute I sat still was a minute lost looking for Rachel. And all those minutes added up could make the difference between reaching her or not; rescuing her or not. If she even needs to be rescued, I thought to myself. The fact that it might be me that needed her help was a possibility too hard to hold on to.

I put my cigarettes and matches on the table and the waiter brought over an ashtray. I offered to move outside, but he waved away my query with a flick of his hand.

‘Please,’ he said, setting an old metal dish between us. ‘No problem.’

Baaz wrinkled his nose. He truly hated cigarette smoke. I should have truly hated him being there. But whether he’d been saved by the last gasp of my conscience or the diligence of his calculations, I was glad he was, all the same. The truth was that it was already too late to protect his family. He’d entered Israel on his own passport, made no attempt to hide his identity from anyone. As far as the Shabak – or anyone else – was concerned, he was up to his neck in it, whatever it was. In Paris he chose not to run; and that choice had consequences.

The waiter came back with our coffees – strong, spiced with cardamom and loaded with sugar – and pieces of sticky baklava.

‘The number on the note,’ I asked Baaz, as he sipped at the tiny cup, ‘what do you think it means?’

‘I don’t know,’ he said.

‘But what’s your gut instinct?’

‘My computer science professor in Chandigarh told me that gut instincts are very bad. There is a right answer and a wrong answer. Correct solutions are arrived at with facts, not hunches.’

‘What absolute bullshit, Baaz. Seriously.’ I shook my head and slurped the thick black coffee carefully, so as not to get a mouthful of the grounds from the bottom of the cup. ‘You’re in the catacombs. There’s been a cave-in. Or a flood. The route has changed. You use what you know to make an informed guess, right?’ He pursed his lips. ‘And don’t tell me you don’t, because I know you do. You’re still alive. No one could spend as much time down there and still be in one piece if they weren’t lucky – at least once.’

He shifted in his chair uncomfortably. I played with the packet of Marlboros.

‘OK,’ he relented, ‘my hunch is that the serial number is too unusual to be a coincidence – especially if you consider that the number itself is from an uncirculated print run. Besides, this man – Moshe? He says that the printer can add any serial number they like to a plate. So maybe that prime has a purpose? As a prime, I mean.’

‘How do you mean?’