Pet nodded in agreement as Tom started the engine and then pressed two hidden switches just below the steering column. A wailing noise erupted from the bonnet area and he engaged the automatic gearbox, speeding off west, weaving through the dense traffic. His face was a mask of pure concentration as the city at rush hour flew past, the blue strobe lights concealed within the grille flashing urgently.

*

The journey to RAF Northolt took just under half-an-hour, the only sound inside the car the wail of the sirens. At Hanger Lane on the A40, Tom pulled into a small cul-de-sac and stashed his iPhone under a loose paving slab beneath a bush. Once at the RAF base he pulled over in the visitor parking bays, removed the keys, and handed them to Pet.

‘Take the car and go somewhere safe where we can stay in contact, and retrieve my phone as quick as you can,’ he said, his eyes fixed on the barrier.

‘Are you sure this is what you want? You know it’s almost certainly a suicide mission.’ She looked at him, her eyes moist.

‘I’ve no choice. My foster family is all I have, and without them I’m all alone. There is no way Branko will let them go, even if I give him what he wants.’

‘But—’

‘There’s no other way, Pet. Take the Sig and go somewhere safe. Be ready for me when I start; I will need your help.’ He grabbed her hand and squeezed it tight for a fraction of a second before opening the door. Pet pulled him towards her and threw her arms around his neck, burying her head against his chest.

‘Promise me you’ll be careful, Tom,’ she said in a faltering voice.

‘Always careful, Pet,’ he said, disentangling himself and fixing her with a smile. The smile didn’t reach his flinty hard eyes, though.

He got out, carrying nothing but the sat-phone, and strode up to the main gate, which was manned by a uniformed MPGS guard armed with an SA80 assault rifle. The guard viewed him with mild interest.

‘My name is Tom Johnson,’ he said, giving his cover name. ‘I understand I’m expected.’

‘Go into the guardroom, sir, and speak to the duty RAF Police.’

Tom went up to the small window of the guardroom at the side of the barrier, where a middle-aged man dressed in the petrol-blue of the RAF sat. Tom noted the epaulette-mounted rank slides of a sergeant, with the red-and-black insignia of the RAF Police.

‘My name is Tom Johnson. Are you expecting me?’ He proffered the driving license and the sergeant took it wordlessly.

‘Wait one moment please, sir,’ he said in a broad Yorkshire accent.

Tom heard the barking of orders from within the guardroom, shortly followed by the sergeant striding out of the door wearing the white-topped flat cap which gave the RAF Police their nickname: ‘Snowdrops’.