“It depends,” she said. “The Admiralty charts were ahead of their time when it came to accuracy, although the earlier ones were privately produced and had lots of errors. The Admiralty certified some maps that shouldn’t have been.”

“You’re saying that an island could be on some charts but not others?”

“Absolutely! The charts and atlases of the nineteenth century showed more than two hundred islands that never existed.”

“How could that happen?”

“Many ways. A land-starved mariner might mistake a cloud formation for an island and record its position. Figuring longitude was also a problem. Someone might mark a real island in the wrong place. Con men created phony islands to push get-rich-quick schemes. The next guy in the neighborhood looks at his chart and sees empty sea where an island should be . . . Now, tell me what you know about your phantom island.”

“I know that it was real,” Zavala said. “An American whaling ship stopped there in 1848. But the island is not on any modern map. There’s an atoll fairly close by, though.”

“I’ll start by looking for an 1848 chart or one close to it,” she said. “Next, you’ll want to compare it to Pacific Chart 2683.”

“What is so special about it?”

“It’s the gold standard of Admiralty charts. The British Hydrographic Office knew that the Admiralty maps were getting out of whack. Accurate charts were essential for the Navy and commercial interests. So, in 1875, the Admiralty brought in a chief hydrographer named Captain Frederick Evans to purge the phantom islands from all their charts. He got rid of more than a hundred islands in the Pacific alone. The corrected chart was designated with the number 2683.”

“Then it’s possible that the island never existed?” he asked.

“Possibly. But islands can disappear. Your island might have sunk into the sea after a volcanic eruption, an earthquake, or a flood. There is historical precedent: the island Tuanah supposedly sank with its inhabitants. And there are other reported cases on record. It could be a reef or rock below the surface now, and even a satellite wouldn’t pick it up. You’d have to get in for a close look.”

“Where do we start?” Zavala asked.

“A lot of this stuff is online,” Beth replied. “The British Library has the biggest collection of Admiralty charts. I’ll go there first, and then I’ll take a look at the UK’s National Archives. If I have to go to the Royal Geographical Society or the Maritime Museum at Greenwich, it might take a while. When do you need this information?”

“Yesterday,” Zavala said. “Lives may depend on what we find.”

“Are you joking, Joe?”

“I wish I were.”

After a brief pause at the other end of the line, Beth said, “Like I told you, I love a challenge.”

Zavala wondered if he had been too dire and tried to lighten the mood.

“Are you married or engaged, Beth?”

“No. Why?’