THEY WERE TEN FEET from the boat when they heard the rumble of diesel engines approaching from behind. They reached the ladder and turned around to see a Tanzanian coast guard gunboat a hundred yards away. Sam and Remi climbed onto the Andreyale's afterdeck and shed their gear.

"Smile and wave," Sam murmured.

"Are we in trouble?" Remi whispered through her smile.

"Don't know. We'll soon find out." Sam continued waving.

"I've heard Tanzanian jails are unpleasant."

"Every jail is unpleasant. It's all relative."

Thirty feet away, the gunboat came about and drew parallel to them, bow to stern. Sam now saw it was an upgraded 1960s-era Chinese Yulin-class patrol boat. They saw Yulins several times on each of their trips, and Sam, ever interested, had done his homework: forty feet long, ten tons; three-shaft, two six-hundred-horsepower diesel engines; and a pair of twin 12.7mm deck guns fore and aft.

Two sailors in jungle fatigues stood on the afterdeck and two more on the forecastle. All bore shoulder-slung AK-47s. A tall black man in crisp whites, clearly the captain, stepped from the cabin and walked to the railing.

"Ahoy," he called. Unlike Sam and Remi's previous encounters with the coast guard, this captain was grim-faced. No welcoming smile or pleasantries.

"Ahoy," Sam replied.

"Routine safety check. We will board you now."

"Be our guest."

The gunboat's engines gurgled, and the Yulin angled closer until its bow was ten feet away. The engines went back to idle, and the Yulin glided to a stop beside them. The sailors on the afterdeck tossed tire bumpers over the side, then reached down, grabbed the Andreyale's railing, and pulled the boats together. The captain vaulted over the railing and landed catlike on the Andreyale's afterdeck beside Sam and Remi.

"You are flying the diver flag, I see," he said.

"Doing a little snorkeling," Sam replied.

"This boat is yours?"

"No, a rental."

"Your papers."

"For the boat?"

"And diving certificates."

Remi said, "I'll get them," then trotted down the steps into the cabin.

The captain asked Sam, "What is your purpose here?"

"On Zanzibar or here specifically?"

"Both, sir."

"Just on vacation. This seemed like a nice spot. We were here yesterday."

Remi returned with the documents and handed them to the captain, who first examined the rental agreement, then their diving certificates. He looked up and studied their faces. "You are Sam and Remi Fargo."

Sam nodded.

"The treasure hunters."

Remi said, "For lack of a better term."

"Are you hunting treasure on Zanzibar?"

Sam smiled. "That's not why we came, but we try to keep our eyes open." Over the captain's shoulder, behind the tinted windows of the Yulin's cabin, Sam saw a shadowed figure. It appeared to be staring at them.

"Have your eyes seen anything on this visit?"

"A coin."

"You are aware of Tanzanian law regarding these matters?"

Remi nodded. "We are."

From the Yulin, a knuckle rapped once on the window.