The drone hovered for a moment more at the edge, turning back to Freddie one last time, who lifted an arm to wave goodbye, and then the drone turned back, and began its descent.

“Diorite batholith, quartz and some granite – damned hard rock,” Greg said, turning to Abby and raising his eyebrows.

“Very good, Professor Jamison.” Abby smiled. “And it’s old; there’s exposed Jurassic-age plutonic rock I can see there. That’s the result of the magmatic arc most probably created by the northwest-directed subduction. What I can see is hornblende gabbro through quartz monzonite, tonalite and quartz diorite.” She smiled, disarmingly. “But like you said, damned hard rock.”

He nodded, mock serious. “I was just going to say all that.”

“Quiet, you two.” Cate threw the words over her shoulder as she frowned at the screen.

There was a soft moan rising from the speakers as the wind moved across the cave mouth as the drone approached. The cave itself was a vertical tear in the rock, about ten feet high, and three wide – narrow.

“We going to fit in that?” Cate asked.

“Just.” Freddie’s voice was distracted.

The drone eased towards the dark opening, and immediately its brilliant lights blinked on. The darkness inside the cave was pushed back and the hovering machine moved carefully into the tear.

“Hold it there… back up, back up.” Cate stood, sat back down, and then half stood again, her neck craned forward. “Slow, slow, rotate ninety degrees to your left.”

The drone backed up to just inside the cave, and the turned in the air. The lights illuminated a large flat wall. The scratched message was still clear. She breathed the words as she read.

“Jim Granger went in here – 12 Oct 52.”

Greg sat back. “So, this is not about your grandfather, huh?”

“I knew it.” Cate made a fist. “I knew he came this way.”

Freddie’s voice filled the room again. “Interesting; outside it’s just on three degrees, but temperature inside the cave mouth says it’s fifty. That’s a massive jump. Got a real hot zone in there somewhere. Okay guys, we’re burning time, so gotta get moving. I’m taking Buzz in.”

The drone moved slowly, the images now compressed down to the width of the cave entrance, until it opened out into a large flat room. Freddie swiveled the drone through a full three-sixty-degree turn.

“Looks to be about a hundred feet in here, give or take.” The drone hung in the air for another few seconds, before zooming ahead. “There’s another opening on the far side – going in.” Freddie now whispered his words as if worried about being overheard. “You should be seeing a thermal readout beside your screen – temperature now about seventy degrees. I’m dropping a relay beacon, so we don’t lose contact with Buzz.”