"No time for that," Pitt interrupted impatiently. "We must get back out as fast as we can and keep searching."

"Excuse me, Major!" Hersong had caught Pitt's arm, an action that surprised Pitt by seemingly coming out of nowhere. "I found something that might be of interest."

The mist went through its cycle and then cleared again, revealing a peculiar expression on Hersong's face that caught Pitt's attention. He grinned at the lanky botanist.

"OK, Hersong, let's make it quick. We hardly have time for a lecture on marine flora."

"Believe it or not, that's just what I had in mind." Hersong grinned back; the glistening water trickled through the strands of his beard. "Tell me, did you notice that growth of Macrocystis pyrifera on the wall opposite the tunnel?"

"I might have," Pitt answered flatly, "if I knew what you were talking about."

"Macrocystis pyrifera is a brown algae of the Phaeophyta family, perhaps better known as kelp."

Pitt stared at him, considering, and let him continue.

"What it boils down to, Major, is that this particular species of kelp is native only to the Pacific Coast of the United States. The water temperature in this part of the Mediterranean is far too warm for Macrocystis pyrifera to survive. On top of that, kelp, like its land plant cousins, needs sunlight to provide the process for photosynthesis. I can't imagine kelp thriving in an underwater cave. Nope, if you'll forgive the vernacular, it just ain't done."

Pitt was slowly treading water. "Then if it isn't kelp, what is it?"

The mist was back, and Pitt couldn't see Hersong's face. He could only hear the botanist's rumbling voice.

"It's art, Major, pure art. Without a doubt, the finest plastic replica of Macrocystis pyrifera I've ever beheld."

"Plastic?" Knight boomed, his tone echoing around the cavern. "Are you sure?"

"My dear boy," Hersong said disdainfully. "Do I question your analysis of core samples or—"

"That red slime on the tunnel walls," Pitt cut in. "What do you make of that?"

"Couldn't say for sure," Hersong said. "Looked like some type of paint or coating."

"I'll back him, Major." The face of Stan Thomas suddenly materialized out of the fading mist. "Red antifouling paint for ship hulls. It contains arsenic; that's why nothing grows in the tunnel."

Pitt glanced at his watch. "Time is running out. This must be the place."

"Another tunnel behind the kelp?" Knight asked in a careful sort of voice. "Is that it, Major?"

"It's beginning to look encouraging," Pitt said quietly. "A camouflaged second tunnel that leads to a second cavern. Now I can see why von Till's operation was never discovered by any native of Thasos."

"Well," Hersong purged the water from his mouthpiece. "I guess we keep going."

"We have no other option," Pitt said. "Are we all ready for another go?"

"All present and accounted for, except for Woodson," Spencer answered.