As Henderson approached the doors at the front of the lobby he pulled the pin from the grenade and dropped it into the earth beneath a potted palm. Marc had never been through a revolving door and looked perplexed, but it wasn’t the right moment to hang around and Henderson gave him an almighty shove before shuffling around inside the door. They stepped out into fresh air and a line of officers smoking and holding glasses of wine. It was almost nine and the sky was purple.

‘Excuse me, gentlemen,’ Henderson said, as he pushed Marc through the line of officers. ‘I must escort this messenger.’

As soon as Henderson broke clear of the officers and started down the steps a German infantryman who looked no more than eighteen stood in front of Henderson, clicked his heels and gave a Nazi salute.

‘Heil Hitler. Do you require transport, sir?’

Henderson was counting in his head and knew that the grenade would explode within four seconds. ‘Something fast,’ he said, pointing towards a motorcycle with a sidecar. ‘Are the keys in the ignition?’

‘Yes, Herr Major,’ the infantryman said, nodding. ‘Fully fuelled and ready to—’

A white flash erupted from the front of the hotel, followed by a shower of glass and smoke that sent a dozen Gestapo officers toppling down the hotel’s front steps. Screams rang from inside as Henderson grabbed Marc and dragged him towards the motorbike.

Henderson felt a sharp pain where a splinter of glass had nicked his ear, but he had to ignore it as he straddled the bike and Marc vaulted into the sidecar. Henderson kicked the starter and he felt the engine vibrate between his legs, but he hardly heard a thing because his ears still rang from the blast.

‘When I stop, you run to the car and grab the bag from the trunk,’ he shouted.

Marc wasn’t sure what Henderson meant, but realised once he’d taken a sharp left out of the hotel driveway and another into the side street where he’d parked his battered Fiat. The boy had one leg out of the sidecar before they stopped at the kerb.

Henderson kept the motorbike running as Marc struggled to open the trunk.

‘Push the button and twist the handle,’ Henderson shouted, as a set of headlights turned into the alleyway behind them.

It only took Marc a few seconds to get into the back of the Fiat, but it felt like minutes. He grabbed Henderson’s briefcase – which contained gold and money – and his own pigskin bag and threw them into the sidecar before jumping on top of them.

Henderson realised that the Mercedes saloon behind them was driving too fast to be routine traffic. It was coming after them, with a brace of motorcycles for company.

‘Use your pistol,’ Henderson ordered. ‘See if you can fend some of them off.’