Marc was delighted that a British agent was going to all this bother on his account. Henderson could have abandoned him at the passenger terminal and sailed aboard the Cardiff Bay with Paul and Rosie. But as well as a soft heart, Henderson had a ruthless streak and the gun made Marc uneasy.

In the three days since Marc first met Henderson in Paris, Henderson had shot or blown up half a dozen Germans and machine-gunned a grovelling Frenchman in his bathtub. If the next figure at the end of the alleyway chose to come and investigate, Marc knew Henderson would kill them without a thought.

Henderson passed over a crowbar before screwing a silencer to the front of his pistol. Marc ran his hand along the oiled bar and glimpsed inside the suitcase: ammunition, a compact machine gun, a zipped pouch in which Marc knew lay gold ingots and a stack of French currency. The clothes and toilet bag seemed like an afterthought, squeezed into the bottom right corner. Marc found it miraculous that Henderson could lift all this, let alone carry it several kilometres through the port.

After fastening leather buckles and tipping the jangling case back on its side, Henderson faced the building and lowered his knee into the puddle. Marc leaned against the wall and stepped up so that his wet boots balanced on Henderson’s shoulders.

‘Now I’m really glad you didn’t tread in that pile of turds,’ Henderson noted.

Despite nerves and his precarious position astride Henderson’s shoulders, Marc snorted with laughter.

‘Don’t make me giggle,’ he said firmly, walking his hands up the brickwork as Henderson stood, raising Marc level with the landing window between ground and first floors.

Marc rested his chest against the wall, then took the crowbar from his back pocket.

‘You’re heavier than you look,’ Henderson huffed, as Marc’s unsteady boots tore at his skin.

The oak window frame was rotting and Henderson felt a shower of flaking paint as Marc dug the forked tongue of the crowbar under the frame and pushed as hard as he dared. The catch locking the two sliding panes together was strong, but the two screws holding it in place lifted easily from the dried-out wood.

‘Gotcha,’ Marc whispered triumphantly, as he threw the window open.

To Henderson’s relief, Marc’s weight shifted as the boy pulled himself through the window. He crashed down on to plush carpet inside, narrowly avoiding a vase and a knock-out encounter with the banister.

Beeswax and old varnish filled Marc’s nose as he hurried downstairs. The building was small, but its pretensions were grand and paintings of wigged men and naval battles lined the short flight of steps down to the back door.