Hacker replied, ‘The more you talk, Hope, the more fun this is going to be.’

They marched Ben deep into the castle’s maze of stone passageways to a studded oak door, from where a flight of steps led down to a basement floor with numerous other doors running off it. From there, a narrower and dingier stairway led further downwards into growing darkness and an intensifying smell of damp. A pair of electric lanterns hung from a recharging station on the sub-basement wall. Hacker and Banks grabbed one each, turned them on and the shadows were chased away by strong bright light. Ben saw a steel door ahead, thick and heavy like something that would protect a bank vault. Carter and Banks backed him against the wall with their fingers on their triggers while Hacker produced a key and used it to open four large, sturdy padlocks holding the door. Stuart wasn’t leaving much to chance, when it came to prisoner security.

Hacker heaved the vault door open, then signalled to Banks and Carter to move Ben along. Hacker went through the door first, backwards with his gun trained on Ben’s chest. Carter and Banks brought up the rear, pointing their weapons at Ben’s back. ‘Nearly there,’ Hacker chuckled to Ben. ‘Bet you must be so happy to see your old mate again.’

They moved on through a stone-block tunnel whose craggy walls were streaked with mould and mildew. A few dozen metres further, a third flight of steps took them still deeper below the castle. Ben guessed they must be right down in the foundations by now.

The Dishonourables were still being extremely careful not to get too close to Ben. He could sense their growing anxiety. They kept moving. Next they reached a steel cage door held fast with more padlocks, which opened into an arched stone tunnel more cramped than the one before it. The swaying lanterns made eerie shadows on the walls. The dank airlessness down here was oppressive. It was like walking back into the darkest, ugliest parts of history. Nothing else about Stuart’s castle felt authentic, but this did. It was easy to imagine the horrors experienced by prisoners of bygone centuries, left to rot and starve in black holes where rats scuttled and feasted on the remains of the dead. Ben thought of Boonzie McCulloch being kept in such a place. The anger only made his resolve stronger.

Then Hacker said, ‘Here we are, boys. End of the line.’

The tunnel was blocked off ahead. Ben had expected something like a barred prison door inset into the end wall, but saw nothing until he looked down at Hacker’s feet and realised that the entrance to the dungeon was an iron grid trapdoor with massive hinges cemented into the floor, and secured by a long bolt. A collapsible aluminium ladder lay beside the opening.