Kurt put his hand to a keypad, typed in 2-5-0, and held his finger over the “Enter” button. Either Kurt or Joe could change the depth manually if they wanted, but the computer was more precise.

“Three… two… one… mark.” Kurt hit “Enter,” and they heard the sound of a small pump as it pushed oil from the rear into a forward chamber of the sub. This caused the nose to grow heavier and pitch down. With no need to take on water, to angle dive planes, or to adjust power, the Barracuda continued at flank speed, descending, and actually accelerating as it dove.

Around them the light began to fade, the color changing from a bright aquamarine to a darker blue. Up above, it was a beautiful sunny day, with high pressure all around.

“How we doing?” Kurt asked.

“Four miles to the outer marker,” Joe said.

“What about the other contestants?”

It was a timed race, the subs having left at ten-minute intervals to keep them apart, but Kurt and Joe had already passed one vessel. Somewhere up ahead they would catch another competitor.

“We could ram them if they get in our way,” Joe said.

“This isn’t NASCAR,” Kurt replied. “I’m thinking that would be some kind of points deduction.” As Kurt kept the Barracuda precisely online, he heard Joe tapping keys behind him.

“According to the telemetry,” Joe said, “the XP-4 is a half mile ahead. We should see his taillights in about ten minutes.” That sounded good to Kurt. The next depth change was in seven minutes. They would come up to one hundred fifty feet, cruise over a ridge, and race along near the top of an underwater mesa — a flat plain that had once been an underwater lava field.

“Easier and more fun to pass people when they can see you go by,” he said.

Seven minutes later, Kurt put the Barracuda into a climb, they zoomed up over the ridge and leveled off at one hundred fifty feet. A moment later the radio crackled.

“… experiencing elec—…—blems… batteries… system malfunc—…” The garbled low-frequency signal was hard to make out. But it rang alarm bells in Kurt’s mind.

“You get that?”

“I couldn’t make it out,” Joe said. “Someone’s having problems though.” Kurt grew quiet. All the subs had been equipped with a low-frequency radio that, theoretically, could reach floating buoys along the race path and be retransmitted to the referee and safety vessels stationed along the route. But the signal was so weak, Kurt couldn’t tell who was transmitting.

“Did he say electrical problems?”

“I think so,” Joe said.

“Call him out,” Kurt said.

A moment later Joe was on the radio. “Vessel reporting problems. Your transmission garbled. Please repeat.” The seconds ticked by with no response. Kurt’s sense of danger rose. To make the submarines fast, most had been built with somewhat experimental technology. Some even used lithium ion batteries that, in rare circumstances, could catch fire. Others used experimental electrical motors and even hulls of thin polymers.

“Vessel reporting problems,” Joe said again. “This is Barracuda. Please repeat your message. We will relay to the surface.” Up ahead, Kurt saw a trail of bubbles. It had to be the wake of the XP-4. He’d forgotten all about it and was now driving right up its tailpipe. He banked the Barracuda to the left and then noticed something odd: the trail of bubbles arced down and to the right. It didn’t make any sense, unless…

“It’s the XP-4,” he said. “It’s got to be.” “Are you sure?”

“Check the GPS.”

Kurt waited while Joe switched screens. “We’re right on top of him.” “But I don’t see him anywhere,” Kurt said.

Joe went right back to the radio. “XP-4, do you read?” Joe said. “Are you reporting trouble?” A brief burst of static came over the radio and then nothing.

“We’ll lose if we turn,” Joe said.

Kurt had considered that. The rules were strict.

“Forget the race,” Kurt said, and he banked the Barracuda into a wide right turn, slowing her pace and manually taking over depth control. Throwing on the Barracuda’s lights, he searched for the trail of bubbles.

“What’s the XP-4 made of?” he asked. Joe knew the other competitors far better than he did.

“She’s stainless steel like us,” Joe said.

“Maybe we could use the magnetometer to help find her. A thousand pounds of steel ought to get us a reading from this distance.” Kurt spotted what he thought was the line of bubbles. He turned to follow the curving, descending trail. Behind him Joe booted up the magnetometer.

“Something’s wrong,” Joe said, fiddling with the controls.

“What’s the problem?”

“See for yourself.”

Joe pressed a switch, and the central screen on Kurt’s display panel changed. The lines of azimuth and magnetic density should have been a relatively clear display, but the various lines were spiking and dropping, and the directional indicator was pivoting like a compass needle just spinning in circles.

“What the heck’s wrong with it?” Kurt mumbled.

“Don’t know.”

The radio buzzed with static again and this time a voice cut through it.

“… continued problems… smoke in cabin… possible electrical fire… shutting down all systems… please—” The transmission ended abruptly, and it chilled Kurt’s blood.

He looked through the curved Plexiglas windshield of the Barracuda, slowing the small submarine even further. As the speed bled off, he pitched the nose over until they were angled almost straight down.

Dropping slowly through the water, he scanned the bottom. At one hundred fifty feet, light from the surface still filters through, but the surrounding color is a pure dark blue, and the visibility is limited to somewhere around fifty feet.

Increasing that visibility were the Barracuda’s lights. Since seawater scatters and absorbs longer wavelengths of light rapidly, Joe had installed special bulbs that burned in a bright yellow-green part of the visible spectrum. The lights helped cut through the gloom, and as the Barracuda approached the bottom Kurt spotted what looked like a gouge in the sandy sediment.

He turned to follow it.

“There,” Joe said.

Up ahead, a tubular steel shape that looked more like a traditional submarine lay on its side. The designation “XP-4” could be seen, painted in large black letters.

Kurt circled around it until he reached a spot from which the canopy could be viewed. Bubbles were pouring slowly from the tail end of the sub, but the cockpit seemed intact.

He shut the lights off and tried to hover alongside, though the current was making it difficult.

“Signal them.”

As Kurt struggled to keep the Barracuda in position, Joe grabbed a penlight, aimed it out the window at the XP-4, and tapped out a message in Morse code.

Kurt could see some movement inside, and then a message came back.

“All… elec… pwr… out,” Joe said, translating.

Kurt felt them drifting again and tapped the thruster.

“They have to have oxygen,” Kurt said, reviewing in his mind the safety rules the event’s organizers had put in place. “Can they pop the canopy?” Joe flashed the light on and off, putting the message through. The response dashed those hopes.

“Canopy… elec… trapped.”

“Who ever heard of making your canopy electric?” Kurt mumbled. Then he looked back at Joe.

“Ours has a manual release,” Joe assured him.

“Just checking.”

Joe smiled. “Can we tow them out?”

“Looks like we’ll have to,” Kurt said. “Use the hook.” Behind him, Joe activated the controls for the grappling system, and a panel on the right wing of the Barracuda opened. A folded metallic apparatus emerged. Once it was locked into place, it unfolded into a long metallic arm with a claw on the end.

Even as the claw extended, Kurt realized they were drifting away from the XP-4.