Eddie tore a bullet from the sleeve and pulled back the charging handle to open the rifle’s chamber. He pushed the round inside and tipped the weapon slightly upwards to minimise the chance of a slamfire – an accidental weapons discharge – then thumbed the bolt release.

Clack! The handle sprang back into place. No slamfire. The M16 was ready for action.

But he only had one shot.

And the guard had heard the unmistakable sound of the bolt closing. He ran into the room, gun raised—

Eddie whipped up the rifle – and fired.

The bullet hit the guard’s chest just as he pulled his own trigger. The impact threw off his aim, the pistol round clanking into a drawer beside the Yorkshireman. The man spun, blood spouting from both the pencil-width entry wound and the much larger exit wound in his back, and fell nerveless to the floor.

Ears ringing, Eddie exhaled. ‘Shit! That was close.’ He picked up the fallen man’s SIG Sauer P320. ‘Get another bullet,’ he told the wincing Nina.

‘What for?’

‘For you. I’ve got this,’ he waved the pistol, ‘so you can have this.’ He held up the rifle.

She collected another round, then joined him. ‘There’s no magazine – it’ll still only have one shot.’

‘One shot’s better than none.’ He quickly reloaded the M16. She reluctantly took it. ‘Okay, we took a wrong turn somewhere. Hopefully the other way isn’t a dead end too!’

They ran back towards the junction as more alarms sounded.

Broates had taken a different route from Nina and Eddie, pushing Eleanor into a machine room. ‘If I remember correctly, this service passage cuts behind the archive wing and leads almost directly to the emergency stairs,’ he said as he let go of the wheelchair and went to a door. ‘We can get ahead of Professor Wilde and Mr Chase. I’ll deal with them.’

‘Good,’ Eleanor replied. ‘But keep her alive if you can. I still need—’

He opened the door – and reeled as dirty yellow gas rushed through it.

Eleanor pulled back on her chair’s control stick in fright as the butler collapsed. ‘Broates!’ she cried, but the cloud had already rolled over the convulsing man. A new alarm sounded as sensors in the machine room detected the contaminant; the service passage, intended only as a conduit for water pipes and electricity cables, had not been similarly equipped.

Panic rising, she spun and retreated at top speed, the chair’s motors whining. With the shortcut blocked, she now had to navigate the whole underground maze to reach the other exit.

An exit with no elevator, only stairs.