Free Code by Kathy Reichs

“the choice was completely arbitrary. Before that conference, mapmakers had used dozens of other places as zero longitude. Rome. Paris. Rio. Mecca. Most countries just picked their own prime meridian.”
    “Is this going somewhere?” Shelton stifled a yawn. “We already tried the digits as coordinates. They pointed to the freakin’ Sahara Desert, remember?”
    “Say these
are
coordinates.” Ben lifted his copy of the clue. “The first number would be latitude. 32.773645. The second would be longitude. -00.065437.”
    “And the closest town is—” Hi glanced down, face smeared with orange debris, “—Bou Semghoun. An oasis village in the Ghardaia region of southern Algeria. Think they get DirecTV?”
    Ben’s eyes twinkled. “Guess what
else
is at latitude 32.773645?”
    “What?” I felt goose bumps prickle my skin.
    “Downtown Charleston,” Ben smacked his hands together. “Booyah!”
    “Get out!” Hiram’s eyes widened. “How’d you know that?”
    “Fishing.” Ben wore a smug grin. “If I find a good spot, I bookmark the location in
Sewee
’s GPS system. I’ve seen latitude 32.77 hundreds of times. I should’ve recognized it as soon as I saw the clue, but the rest of the string threw me.”
    “But we still need a longitude,” Shelton pointed out. “We can’t find anything without both numbers.”
    Ben’s smile widened. “Got that, too.”
    “Spill it,” I demanded.
    “That’s why I brought up the prime meridian,” Ben said. “Zero degrees longitude
doesn’t have to be fixed to Greenwich.
Not like zero latitude, which is always fixed to the equator and can’t move.”
    I saw were Ben was going. “So this longitudinal coordinate could rely upon some other prime meridian. A totally different starting point!”
    Ben leaned back, hands behind his head. “Bingo.”
    “But that could be anywhere,” Shelton whined. “Literally any point on earth.”
    “Wait, wait!” In his excitement, Hi spilled nacho chips onto his keyboard. “This clue was hidden inside the geocache. On Loggerhead! And that’s the only fixed location the Gamemaster gave us.”
    “Hi figured it out,” Ben grumbled. “Sometimes I hate how smart you guys are.”
    Alone in his bedroom, Hi raised the roof.
    “So we use the first number as a normal latitude.” Dots were connecting for me. “Then we assume the second coordinate is for longitude, but with the Loggerhead cache location as the prime meridian.”
    Ben nodded. “That’s our new zero longitude.”
    “Ben, that’s brilliant!”
    Suddenly, the boy was all blushes. “No big deal. Easy, really.”
    “So where does—” I scanned quickly, “—longitude -00.065437 lead now?”
    “You’ve got mail.” Ben tapped his mouse.
    The message arrived almost instantly. I opened the lone attachment and loaded a JPEG onto my desktop.
    And knew.

CHAPTER 11
    “C astle Pinckney?” Shelton’s voice was skeptical. “It’s abandoned, has been for years.”
    “These coordinates are dead-on,” Ben said firmly. “No way that’s by accident.”
    “But there’s nothing out there.” Shelton frowned into his webcam. “Just a beat-up pile of old rocks.”
    “Part of the building still stands.” Hi’s gut filled a quarter of my screen as he searched above his desk. “I’ve got a book here, somewhere.”
    “Sounds like a good spot to hide something.” I pulled up images as I spoke. “What do we know about the castle?”
    “Hold on a sec,” Hi called from off camera. “Must be in my closet.”
    My search results were not inviting.
    Castle Pinckney was definitely deserted, and the neglect showed. A gnarly tumble of broken masonry and chest-high weeds, the dilapidated fort occupied a tiny atoll in the middle of Charleston Harbor.
    The main building was circular, with a high curtain wall facing the harbor mouth. Scrub forest grew close, like a wild, tangled beard. Dark vines covered the crumbling gray stone, locking the fortress in a choking, shadowy