When she couldn’t hold her breath any longer, she rolled gently onto her back and exhaled, drew another long breath, then returned to her “dead man’s float” pose, drifting downstream like a corpse. Every time she held her breath she counted the seconds carefully to sixty. Then she counted the minutes each time she rolled over for a breath. Fifteen minutes passed quickly, then thirty minutes. She used the time to plan her next move. Once I reach shore, I should follow the river back, she decided, recalling her survival training. The captain will send someone to look for me, and that’s where they’ll start.

As her strength recovered, she took the opportunity to make an inventory of her equipment. The strap of her tricorder had broken shortly after her first run-in with submerged rocks in the rapids. Her fingers found only an empty loop of fabric where her communicator should have been. Only her small hand phaser was still securely in place. Figures, she thought. My least favorite piece of equipment is the only one I’ve got left.

Rolling onto her back at the thirty-five-minute mark, she started to wonder if she might be recovered enough to make an attempt for land. Then she heard the soft wash of white noise getting louder ahead of her. Twisting herself to face forward, she saw light low on the horizon and realized that the landscape was beginning another steep decline. She was drifting toward another run of rapids, and there would be no time to reach land.

The water around Theriault became turbulent, and where the river narrowed it churned itself white with violence and swallowed her whole. Adrenaline coursed through her body as she kicked and flailed against the water, unable to find air, unable to see, hearing nothing but the roar of water crashing over rocks and against itself.

Then she ricocheted off one enormous rock, caromed off another, scraped roughly along the bottom, and broke free for a fleeting moment. She had just long enough to pull one desperate breath of air and realize that the river was racing down a steep gradient and disappearing into a broad, cavelike opening in the side of a hill.

Panic fueled her frantic attempts to defy the current and strike out for the riverbank, which was dozens of meters out of reach. A dip of the riverbed dunked her underwater, and her head struck a rock as she was towed past. Dazed and blinking painful colors from her vision, she suddenly found herself in the dark. The river had gone underground and taken her with it.

No more points of reference, no more parallax along the riverbank to gauge her motion. Pure blackness engulfed her, frigid, merciless, and endless. Inside the subterranean channel the roar of the water echoed back upon itself, a deafening wash of noise so mighty that she no longer heard her own frightened splutters and gasps.

She kicked downward, hoping to hit a shallow patch or a sandbar, anything that might let her stop her inexorable forward motion, but the river hurtled through the stygian depths, its embrace deep and cold. Keeping track of time was a lost cause now. There was only fear and darkness. Then, as she bobbed upward for air, her head collided with the rocky roof of the cavern. Reaching up, she felt it close above her, slick with slime. The river’s passage through the underdark was running out of breathing room.

There was no way to hang on to anything. Every surface she grasped was coated in the same slippery mess, and the roof grew closer by the minute. Theriault kicked as hard as she could to keep her mouth and nose above the water, but the tunnel dipped and curved without warning in the blackness, and she had to cough out one mouthful of water after another. With the space above her narrowing to a sliver, she sucked in one full chest of air, then submerged and let the current carry her away.

Watery silence, no air to breathe. Just the rapid beating of her own heart growing slower as her lungs filled with carbon dioxide. Holding in the expiring breath was too much effort. She let it go slowly, a few bubbles at a time, reluctant to exhale because she knew that her body would reflexively try to inhale immediately afterward…and she knew that would not be possible.

One bubble at a time, one breath escaping, then another, like a prison break from her lungs. Letting go of her last breath was a relief, a surrender, an admission that it was time for the end to begin. A final push, and her chest was empty.

She resisted. Tried to will herself not to breathe in. Squeezed her eyes and prayed that she could just fade away without having to feel the water invading her lungs.

Her chest expanded, and she choked down on the reflex, fought it. It was too strong. Defying her will, her body breathed in. The water flooded her sinus, gagged her, assaulted her. A spasm sealed her airway, and water poured down her throat into her stomach. Terror overcame her training, and she kicked and twisted wildly, desperate to discover some hidden pocket of air, irrationally hoping to find one more fresh breath with her hands.

Involuntarily gulping water, she lost all sensation of her body. Darkness melted into vivid colors, bursts of turquoise and crimson, emerald and chartreuse. A siren’s song called to her.

Then she was free, released into open air.

She was falling, shot out of the stone tunnel by a jet of water and plummeting beside an ivory cascade of spray, toward a cerulean pool fifty meters below. Unable to scream or even breathe through her spasm-sealed airway, she marshaled her wits long enough to tumble into a feet-first position, pinch her nose shut, and cover her mouth before she made impact.

Her body sliced through the water like a blade, sank in a straight line, and came to a stop in the deep pool. Fighting against the weight of the water and the pull of gravity, Theriault kicked and stroked her way to the surface. For several seconds, she struggled to tread water and pull in a breath. Despite being free of the underground river, her body was still trapped in its panicked state. Then her throat relaxed, and she coughed out huge mouthfuls of icy water, clearing the way for the sweetest breath of air she had ever tasted.

Floating in the still waters of the enormous pool, she turned slowly and surveyed the space that yawned around her. It was a staggeringly huge cavern, two kilometers wide and a few hundred meters tall. All around the cavern, massive jets of water erupted from natural-looking tunnels in the walls and fell in majestic plumes to the deep, wide pool. Multiple entrances to a labyrinth of other caves gave the cavern’s walls a honeycombed appearance. The pool emptied into a vast, high-ceilinged tunnel that led deeper underground. High overhead, the dome of the cavern’s ceiling was open, revealing a sky streaked with the painterly hues of a subtropical sunset.

Using slow, steady strokes, Theriault swam to shore, crawled onto the sandy ground, and collapsed. She was grateful to be free of the water, to be tasting air, to be alive. It took her several minutes to notice that she was shivering violently. Looking at her hands, she saw that they were almost blue. Hypothermia, she realized. Have to work fast, before I lose consciousness. She looked around and spotted several large rocks. In her exhausted, battered state, dragging several heavy stones into a line beside a small nook in the cavern wall was a labor of desperation. She assembled enough to make a row as long as she was tall, then crawled into the nook behind the rocks and drew her phaser.

A quick check of the device confirmed that its outer casing was intact. She hoped that it was as waterproof as its specs claimed, and she primed it to fire.

Short, controlled bursts on a low setting swiftly turned each rock orange-hot. That’ll do, she decided.

She tucked her phaser back onto her belt and let herself start to drift off. Basking in the warm glow of the rocks, she decided that, though her phaser used to be her least favorite piece of equipment, it had just become her new best friend.