‘Should set the cat among the pigeons,’ Henderson gasped, as they raced down the stairs with the alarm ringing in their ears.

There were two flights between each floor and as they reached the fifth floor a Gestapo officer in a dressing gown was peering down the hallway, wondering if the alarm was for real. Henderson took aim with the machine gun, but the magazine jammed. At the same moment one of the guards above them leaned over the banister and blasted several automatic rounds, tearing chunks of soft plaster out of the wall and shattering a tall window.

Henderson ditched the machine gun and used his silenced pistol to kill the German standing in the doorway. More random shots came from above as the pair made it down to the fourth floor, where a small group of German officers stood on the landing.

‘French troops,’ Henderson shouted, hiding his pistol as he pointed upwards and tried his best to sound like a panicked maintenance man. ‘They’ve shot two officers and started a fire.’

Marc barged through the crowd with his German pistol tucked inside his trousers. The Germans dived for cover as more bullets rained from above. One daring officer decided to go upstairs and investigate. He was machine-gunned by a green-uniformed guard coming the other way before he made it up three steps.

All Marc could hear as he made it to the third floor was a lot of swearing and yelling in German. Men were filing out on to the staircase, some heading up to investigate the shots and screams up on the next landing, some evacuating because of the fire alarm and the remainder milling about looking as if they needed someone to give them orders.

Henderson reckoned the staircase would become dangerous when the Germans stopped arguing and worked out who they were really after, so he led Marc through the double doors and into a corridor identical to the one they’d evacuated three storeys further up.

‘Don’t run,’ Henderson said, as he slowed to a brisk walk.

Because of their hotel uniforms, the Germans they passed in the hallway accepted their presence and some even looked to them for advice.

‘Probably just a false alarm, sir,’ Henderson explained, sticking to French because it might be suspicious if he used his near perfect German. ‘Go downstairs to the lobby and the fire marshals will direct you out of the building.’

Once they’d passed a dozen rooms and two sets of swinging doors, Marc reckoned they were relatively safe.

‘Chaos is the best disguise of all,’ Henderson said.

Immediately ahead of them, a door clicked open and a young Gestapo officer emerged from his room, buttoning his tunic. His movements were calm and he clearly assumed that the fire alarm was fake.

‘What’s happening here, gentlemen?’ the officer asked.