‘Liam, don’t be like that.’

‘It’s OK, Dad,’ said Liam quietly. ‘No big deal.’

Shepherd looked at his watch. He didn’t have time to argue. He hurried back downstairs and picked up the keys for the X3. ‘I don’t know how long I’ll be, Katra,’ he said.

‘Dan, you’d better take the CRV,’ said Katra. ‘The BMW is booked in for a service tomorrow.’

‘No problem,’ said Shepherd, taking the CRV keys instead. He picked up his mobile and started dialling as he hurried out to the car.

Shepherd drove the CRV to the SAS barracks and showed his MI5 identification card to a uniformed guard, who waved him through immediately, pointing towards a field where a helicopter was already warming up.

Shepherd parked his car and ran over to the helicopter. It was a Eurocopter Dauphin painted in civilian colours and with a civilian registration, but the two pilots were from 8 Flight Army Air Corps. The non-military configuration allowed the SAS to move around the country without attracting attention, and was also used to fly troops in and out of Northern Ireland during counter-terrorism operations.

‘Spider!’ Shepherd turned to see the Major jogging towards him in a black Adidas tracksuit.

‘Thanks for arranging this, boss,’ shouted Shepherd over the roar of the twin engines.

‘No sweat. It’ll have to be a one-way trip because we need it for an exercise tomorrow.’ He clapped Shepherd on the back. ‘Pity you won’t tell me what’s up. Never thought you’d go secret squirrel on me.’

‘I’ll tell you when I get back,’ said Shepherd, and he climbed into the helicopter. The pilot in the left-hand seat turned around and flashed Shepherd a thumbs-up. Shepherd grinned as he recognised the man; they had flown together almost ten years earlier on a training exercise in the Brecon Beacons.

Shepherd slammed the door shut and was strapping himself in when the engine roared and the helicopter lifted off.

The flight to London took just over half an hour, the last five minutes curving along the River Thames until they reached the London Heliport, between Battersea and Wandsworth bridges.

The moment the helicopter landed Shepherd had the door open and was out on to the tarmac, bent low as the rotor wash tugged at his hair and clothes.

A blue-grey Nissan Primera was waiting for him, a black-suited driver ready with the rear passenger door open. There were two Metropolitan Police motorcycle cops in full-face helmets and fluorescent jackets, one at the front of the car and one at the back. Shepherd hurried over and showed his ID to the driver.

‘We’re going to Thames House, right?’ asked Shepherd.

‘Mrs Button wants you at Vauxhall Cross,’ said the driver.

‘She knows best,’ said Shepherd. ‘But I don’t have time to sit in traffic.’ He asked the cop at the rear of the car to hand over his full-face helmet, which he did reluctantly. Shepherd jammed the helmet on his head and climbed on the pillion of the first bike. ‘Let’s go,’ he said. The cop revved the engine and they roared off.