Hunter and Jack spent the better part of an hour searching the reaches of the cavern for an exit. Far behind them in the dark, the Fomorii hunted through the field of bones, drawing closer with every passing minute.
The sign would have been easy to miss if Jack had not been resting his forehead against the rock to calm his mounting panic. Faint vibrations rippled through the wall, a steady, rhythmic beat. He called Hunter over, who pressed his ear to the damp rock.
'You can hear it,' he whispered. 'Boom-boom-boom, like machinery.'
'In here? What could it be?'
When Hunter edged along the wall in a particular direction, the beat grew fractionally louder, until he could hear it clearly. At that point, he spied handholds in the rock leading up to a small, dark opening about ten feet off the ground. Boosting Jack up, he followed him into a tunnel large enough for them to stand upright, cut through the rock. The beat emanated from somewhere ahead.
The tunnel wound steadily upwards, presenting occasional rough-hewn steps for them to climb, the beat growing louder the closer they drew to the source. Soon it was ringing off the stone walls and vibrating beneath their feet.