Substrate

The deeper you go, the hungrier it gets.

Beneath the parched crust of the Nevada desert lies the Aos Si cavern system-a jagged, uncharted fissure that has beckoned cartographer and extreme caver Kaelen Rigg for years. With a hand-picked team of specialists, including geologist Dr. Aris Thorne and survivalist Liam O’Connell, Kaelen descends into the dark, eager to map the unmappable.

But Aos Si is not like other caves. The squeezes are impossibly tight, forcing the team to exhale just to inch forward. The limestone walls are warm to the touch. And the draft that guides their path isn’t airflow from the surface-it is a rhythm. A breath.

As the tunnels contract and shift around them, Kaelen realizes the horrific truth: they haven’t entered a geological formation. They have entered a throat. The Aos Si system is a dormant, mountain-sized organism, and they have just woken it up.

Trapped miles beneath the surface in a digestive tract made of stone, the team must race against the crushing peristalsis of the earth itself. There is no climbing back up. The only way out is through.

A suffocating masterpiece of geological horror, Substrate will make you hold your breath until the very last page.