Despite his apparent serenity, Austin knew that each passing minute diminished the possibility of a flotation-bag ascent. The bathysphere could rely on battery power for light, but its air would eventually peter out. He waited a few more minutes, then called the captain and recommended that they launch the ROV.

The remotely operated vehicle, or ROV, has become the workhorse of undersea exploration. Controlled by means of a tether, an ROV can dive deep, maneuver into the tightest spaces, and transmit television images, allowing the operator to travel to the depths without leaving the dry comfort of the ship.

The captain had chosen a medium-sized vehicle, about the size and shape of an old steamer trunk, that could operate at a depth of six thousand feet. Six thrusters positioned the vehicle with pinpoint accuracy; it was equipped with two manipulators for collecting samples, and several cameras, including high-resolution color video.

A telescoping starboard boom swung the ROV off its cradle and lowered it into the sea. Austin watched it sink under a mound of pale green bubbles, trailing its tether behind it, then stepped into the remote-sensing control center located in a cargo container on the main deck.

The video feed through the ROV’s tether was connected to a console from which the remote’s movement was controlled by a pilot with a joystick. Images from the feed were transmitted to a big screen above the console. The ROV’s heading and speed were displayed in combination letters and numbers at the top of the screen, along with elapsed time.

Moving in a descending spiral, the ROV traveled in minutes the same distance it had taken the bathysphere hours. The remote blasted through schools of fish, scattering them like leaves, as it corkscrewed into the sea.

“Leveling out,” the pilot said.

She put the remote into a shallow-angled dive like an airplane preparing to land. Its twin searchlights picked out brownish green bottom vegetation that looked like leaves of spinach undulating in the current. There was no sign of the Bathysphere 3.

Austin said, “Start searching, in parallel passes, a hundred feet long.”

The ROV cruised about twenty feet over the vegetation. It finished its first hundred-foot pass, then traveled back with fifteen feet separating it from the first pass. The speed indicator showed the ROV was doing five knots.

Austin clenched and unclenched his fists, impatient with the glacially slow pace. Other crew members now gathered around the screen, but no one spoke except for the quick communication between Austin and the ROV pilot. Austin mentally excluded everything in the room, pouring himself into the monitor as if he were riding atop the ROV.

Five more minutes passed.

The ROV’s methodical back-and-forth movement was similar to that of a lawn mower. The picture transmitted by its electronic eye was the same unchanging monotonous carpet of brownish green.

“Wait,” Austin said. He had seen something. “Go to the left.”