He took a quick gulp of air, flipped over, and dove, his head disappearing beneath the surface just as the dinghy’s side tube exploded with a whoosh. The water rippled above him and in the corners of his eyes he saw bullets arcing through the water leaving trails of froth in their wake. The dinghy trembled with each bullet impact, popping and hissing, then collapsed in on itself and slipped beneath the surface, the trolling motor dragging it down stern first.

Sam kicked his legs hard, arms spread wide as he pushed and pulled himself toward the cave entrance. The firing stopped for two seconds—Sam thought, reloading—then resumed, peppering the surface like hail, the bullets penetrating four feet before their thrust fell off and they fell harmlessly to the bottom. Everything went dark as he slipped beneath the rock arch. The pop-pop-pop of gunfire and the thumping of rotors became muffled.

He rolled over and kicked upward, hand groping for the ceiling. Rope . . . rope . . . come on. . . . He felt something brush his feet: the dinghy. Sinking toward the bottom, it had been caught by the cave’s inflow. He felt a tug on his belt as the painter line went taut, felt himself being dragged along. He was distantly aware of muffled gunfire continuing outside. His fingers touched the rope; he drew his dive knife from its calf sheath and sawed through it. Then he was moving, being sucked inside.

Lungs aching, head pounding from oxygen deprivation, Sam fumbled, trying to knot the rope around the knife’s haft. The knife slipped from his fingers, bumped off his chest. He caught it, tried again, managed to work a square knot, then kicked for the surface and broke into air. To the right, in the corner of his eye, he saw Remi clinging to the rock wall. He felt the vortex seize him, start pulling him along.

“Sam, what—”

“Gimme all the slack you got!”

Sam tossed the knife in a high arc that took it up and over the catwalk. As it plunged into the water he was already kicking that way, hand reaching for the rope. Suddenly he was jerked away from it, toward the wall, as the dinghy was pulled deeper into the circular current.

“Remi, the rope, throw it!”

“Coming!”

He heard splashing, saw her stroking behind him. The dinghy was full deadweight now. He was jerked beneath the surface; water gushed into his mouth and nose.

“Grab it!” Remi called. “Right in front of you!”

Sam felt something brush his cheek and he slapped at it. His fingers touched the rope and he closed his fist around it. He jerked to a stop.

He caught his breath, waiting for the sparkling behind his eyes to subside, then looked over his shoulder.

Remi was hanging half out of the water from the other end of the rope. The dive light dangled from her belt loop, casting dancing shadows over the walls.

“Nice toss,” Sam said.

“Thanks. Are you okay?”

“Yeah, you?

“Just barely.”

They hung still for a few moments, getting their bearings, then Sam said, “I’m going to hoist you up to the catwalk. Tie off the rope and then I’ll join you.”

“Right.”

Remi’s triweekly ninety-minute power yoga and Pilates sessions showed their value in spades as she shimmied up the rope like a monkey, then rolled onto the catwalk. The planks gave a sharp pop, followed by a slow splintering sound. Remi froze.

“Spread yourself flat,” Sam said. “Distribute your weight—slowly.”

She did so and then, using her knees and elbows, put some test pressure on the boards until satisfied none were going to give way. “I think we’re okay.” She shed her fins, secured them to her belt, then tied off the rope.

“I’ve got the dinghy and all our gear hanging from my belt,” Sam said. “I’m going to try to save it.”

“Okay.”

Between Remi’s knot and him there was only twenty feet of exposed rope; the rest was trailing in the current. Sam reeled in ten feet of rope, fashioned a temporary waist harness, and then, working by feel alone, secured a closed clove hitch around his belt and the knotted end of the painter line. Right hand clenched around the line above his head, he pulled the release loop on the harness. With a wet zipping sound, the rope went taut. It lifted from the surface, trembled for a few seconds, then steadied.

“I think it’ll hold,” Sam called, then climbed the rope and rolled onto the platform beside Remi. She hugged him tightly, damp hair splayed over his face.

“I guess that gunfire answered our question,” she whispered.

“I’d say so.”

“You sure you’re not hit?” Remi asked, eyes and hands probing his chest, arms, and stomach.

“I’m sure.”

“We’d better get a move on. Something tells me they’re not done yet.”

While Sam knew Remi was almost certainly right, he also knew they had few options: go out the way they’d come in, find another way out, fight, or hide. The first option was a nonstarter—it would play right into their pursuers’ hands; the second option, a huge question mark—this cave system could be a dead end for them, both figuratively and literally; the third, also a nonstarter. While they were armed with Guido the Shoemaker’s snub-nosed .38 revolver, Kholkov and his men were armed with assault rifles. The fourth option, to hide, was their only viable chance to get out of this.

The question was, how long would their pursuers wait before following them here? They had one thing on their side, Sam realized, checking his watch. The inflow period was ending; in a few minutes the current would start flowing out again, making entry difficult.

“So this is what passes for a makeshift secret Nazi submarine pen,” Remi said, shucking off the remainder of her gear.

“Probably so, but there’s no way of telling until we find—”

“No, Sam, that wasn’t a question. Look.”

Sam turned. Remi was shining the flashlight on the rock wall above the pier. Clearly homemade out of pounded tin and paint that had long ago lost most of its color, the four-by-three-foot rectangle was nonetheless recognizable.

“Kriegsmarine Nazi flag,” Sam whispered. In his hurried survey of the cavern, he’d missed it. “The pride of home ownership, I suppose.”

Remi laughed.

Taking it one careful step at a time, probing for weak spots as they went, they made their way across the catwalk to the pier; aside from a few nerve-wracking creaks and pops, the planking held firm. The cables, though coated in a thick layer of slimy rust, were similarly solid, bolted into the ceiling and rock walls by thumb-sized steel eyelets. Under the helpful beam of Remi’s flashlight, Sam recrossed the catwalk, grabbed the rope, and returned to the pier, dragging the submerged dinghy along. Together they hauled it up onto the pier. While the dinghy itself was shredded, the motor and attached gas can had miraculously survived with only a few bullet scrapes. Similarly, of their two dry bags, one was riddled with a dozen or more holes, the other unscathed.

“We’ll sort through this, see what we can salvage,” Sam said.

They walked to the end to have a look at the rear wall. The second chamber was, as Sam had suspected, a fracture-guided system. While thousands of years of water erosion had smoothed the walls of the main cavern, the secondary chamber had jagged and wildly angled walls. At the juncture were two tunnels in the shape of a wide V, one tunnel slanting upward to the left, the other slanting downward to the right. Water sluiced from the left-hand tunnel, half its volume coursing into the main cavern, the other half disappearing down the right-hand tunnel.

“There’s your river,” Remi said.

“It can’t have been here long,” Sam replied. “Walls are too rough.”

“How long, do you think?”

“No more than a hundred years, I’d say. Here, let me see the light. Grab my belt loop, will you?” Remi did as he asked, leaning backward as Sam leaned forward. He shined the light down the right-hand tunnel, then said, “Huh. Okay, reel me in.”