He raised her to her feet. They backed towards the vehicles. He saw Pollard and Smith supporting Bourne between them. Meredith unlocked the Volvo, opened the rear door. Pollard and Smith manoeuvred Bourne’s body on to the seat. Ann examined a deep gash on his head, attempted to staunch the copious bleeding with a clean handkerchief. Even as she worked, Bourne recovered consciousness.

They had got off extraordinarily lightly, Paul thought. He knew already his left wrist was broken. Bourne might show concussion effects later and had a head wound that probably required stitching. But apart from that they seemed unhurt. He looked at Ardvreck House, roasting in its own funeral pyre, remembered the colossal power of the explosion and shivered.

If they had delayed a minute longer before quitting the house. Or if they had not been keeping watch throughout the night. He thought of them sleeping upstairs while that thing with its diabolical power heaped up its barricade of kitchen furniture, moved the gas cylinders to the cellars and turned them on. None of them would have escaped alive.

With his arm around Carol he watched the flames consume the house. In the furnace heat snow melted and cascaded as water from the roof. The wet gravel of the driveway was fast appearing from beneath its retreating coat of white. The fire had a grip on the second floor now. Sheets of flame were pouring from the bedroom windows; the roar of the conflagration was louder.

Pollard approached them, shouting something.

‘We’d better get the cars farther down the drive. If the front of the house falls outwards – ’

He nodded, was about to search for his keys when he froze. A gust of wind parted the smoke, revealing the windows of the tower room. To his horror he saw a figure at the window gazing down at them, the same figure of the clean-shaven burly man he had seen on the morning Carol and he had tried to get away from the house. Hands behind his back, the figure at the window stood motionless and impassive while smoke and flames billowed past him.

‘Pollard! Look!’ He seized Pollard’s arm, almost dragging the army man round while he tried to point with his left. Pollard’s breath hissed in. Paul knew with strangely mixed feelings of satisfaction and fear that Pollard also saw the figure. He too saw a man stand at a window ringed with flames, in a furnace heat where no living thing could have survived.

Suddenly the first floor collapsed. The thunder of its fall was followed by the renewed roar of the inferno as it attacked the upper part of the house. The windows still unbroken were exploding outwards. A solid wall of flame shot from the tower windows and the figure was gone.