They turn and follow the trail upstream, keeping to the plume's edge more by touch than sight. The ambient grumble swells to full-blown cacophony, resolves into a dozen different voices; pile-drivers, muffled explosions, the sounds of cement mixers. Clarke can barely think above the waterborne racket, or the rising apprehension in four separate minds, and suddenly it's right there, just for a moment, a great segmented tread climbing up around a gear wheel two stories high, rolling away in the murk.

"Jesus. It's fucking huge." Brander, his vocoder cranked.

They move together, aiming their squids high and cruising up at an angle. Clarke tastes the thrill from three other sets of adrenals, adds her own and sends it back, a vicarious feedback loop. With their lamps on minimum the viz can't be more than three meters; even in front of Clarke's face the world is barely more than shadows on shadows, dimly lit by headlights bobbing to either side.

The top of the tread slides below them for a moment, a jointed moving road several meters across. Then a plain of jumbled metal shapes, fading into view barely ahead, fading out again almost instantly; exhaust ports, sonar domes, flow-meter ducts. The din fades a little as they move towards the center of the hull.

Most of the protuberances are smoothed back into hydrodynamic teardrops. Close up, though, there's no shortage of handholds. Caraco's smoldering headlight is the first to settle down onto the machine; her squid paces along above her. Clarke sets her own squid to heel and joins the others on the hull. So far there's been no obvious reaction to their presence.

They huddle together, heads close to converse above the ambient noise.

"Where's it from?" Brander wonders.

"Probably Korea." Nakata buzzes back. "I did not see any registry markings, but it would take a long time to check the whole hull."

Caraco: "Bet you wouldn't find anything anyway. If they were going to risk sneaking it this far into foreign territory they wouldn't be stupid enough to leave a return address."

The rumbling metal landscape pulls them along. A couple of meters up, barely visible, their riderless squids trail patiently behind.

"Does it know we're here?" asks Clarke.

Alice shakes her head. "It kicks up a lot of shit from the bottom so it ignores close contacts. Bright light might scare it, though. It is trespassing. It might associate light with discovery."

"Really." Brander lets go for a moment, drifts back a few meters before catching another handhold. "Hey Judy, want to go exploring?"

Caraco's vocoder emits static; Lenie feels the other woman's laughter from inside. Caraco and Brander leap away into the murk like black gremlins.

"It moved very fast," Nakata says. There's a sudden small blot of insecurity radiating from inside her, but she talks over it. "When it first showed up on sonar. It was moving way too fast. It wasn't safe."

"Safe?" Lenie frowns to herself. "It's a machine, right? No one inside."