From the last reading Borshov had taken, the Americans had been just over three miles in the lead, but at their current speed he expected to catch them quickly. He listened again for their footfalls and looked down at the small box for its directional readings. Good, they were still closing, now just over two miles between them. South-south-east with a slightly increasing descent—they must be climbing down at some sections. As Borshov was about to pull his device free from the stone it began to reset before his eyes. It had found another source of resonance. The figures increased rapidly until they stopped at numbers indicating a distance of about two miles, but nearly ninety degrees straight down, and shifting. Borshov closed his eyes to concentrate on the sounds; significant mass, liquid, moving. He pulled the device free. Underground river, he thought.

He gave a short sharp whistle to his agents and sped on again into the dark.

Monica was walking lightly beside Matt, alert to her surroundings, but from time to time dropping deeply into her own thoughts. Be careful, be silent, touch nothing, leave nothing behind; her caving experience made it all automatic now. She used to like nothing more than entering a pitch black cave for the first time, turning out her light and just standing there in the dark, opening her arms wide and just feeling. She would use all her senses other than sight to draw in all the smells, the minute sounds, and feel the weight of the stone around her. She’d done it dozens of times so why now did the thought of switching off her light in this cave give her a knotted, uncomfortable feeling deep in her stomach.

Matt turned towards her and could see the troubled look on her face. “Penny for them.”

“It’s nothing,” Monica said softly.

“Come on, tell Uncle Matt.”

“OK, remember how I said that caves were like people?”

“Hmm, yeah, some are easy, some are bitches; sounded like a few girls I knew in high school.”

“And some are secretive, that’s right. Well, this one is more than secretive; it’s hiding something and for the first time in my life I don’t feel comfortable in the dark.” Matt smiled at her and put his arm around her shoulders.

“Monica, if you’re ever looking for an excuse to get me to put my arm around you just ask, OK?”

“You oaf,” Monica said through a little smile, but didn’t push his arm away.

Alex was the first to catch up to Mike. “What’ve we got?” he asked while looking down over the lip of the drop-off.