Dead Reckoning

by David Garrison

When Ryan Mack's older brother Danny dies in a diving accident off the coast of Honduras, the official verdict is misadventure. Ryan doesn't believe it. Neither did Danny.

Waiting for Ryan in Tampa is a locked Pelican case. a USB drive, a photograph of a man he doesn't recognise, and a handwritten note in Danny's careful script. I think you'll know what to do with this.

What follows is a hunt that will take Ryan from a Tampa kitchen table to the Colombian Caribbean, through five interlocking layers of encrypted clues hidden in plain sight across the a dead man's Instagram account, a self-published book about coral with seven deliberate errors in its index, a Spotify playlist whose description is gibberish unless you know what to look for, a Garmin dive computer account logging 847 dives, and a 1973 Jacques Cousteau hardcover with a secret that only becomes visible under ultraviolet light.

The map was built by Marco Salcedo, a marine biologist who spent seven years hiding his life's most dangerous work inside the ordinary texture of his existence. The treasure at the end of it is two hundred kilograms of uncut Colombian emeralds sitting in a military-grade case at thirty-one metres depth, locked to the frame of a narco-submarine that went down in a Caribbean storm in 2003 and has been waiting there ever since.

So has the man who wants it back.

Ryan is twenty-two years old and has no business doing any of this. He does it anyway, with his best friend Joel, a computer science student who can break any cipher but gets seasick, and an ex-Navy SEAL named Cole Hadley whose interest in the operation goes considerably deeper than his share of the emeralds.

Dead Reckoning is a modern Treasure Island for adult a novel about maps and codes, loyalty and loss, the Caribbean in July, and what it costs to follow a thread to the end when the thread leads somewhere dangerous.

The map is real. The clues are hidden. Some of them are still there to find.

313 pages, Kindle Edition

Published February 28, 2026

About the author

For 25 years David Garrison has served as a missionary with the Southern Baptist International Mission Board. His assignments have included Associate Vice President for Global Strategy, Regional Leader for South Asia, Interim Regional Leader for Central and Eastern Europe, and Interim Regional Leader for Northern Africa and the Middle East. Prior to that, Garrison directed the work of the International Mission Board’s Cooperative Services International program which opened new work among 40 previously unengaged people groups. Garrison’s quest to understand and join God’s global mission has led him to study a dozen languages and visit more than 80 countries, serving as a missionary in Hong Kong, Germany, France, England, Egypt, Tunisia, and India.

Garrison has degrees from Ouachita Baptist University (B.A., 1979), Golden Gate Baptist Theological Seminary (M.Div.,1982), the University of Chicago Divinity School (Ph.D., 1988).

Garrison has taught at Hong Kong Baptist University, Southwestern Baptist Theological Seminary, Fuller Theological Seminary, Trinity Evangelical Seminary, and Columbia Biblical Seminary, in addition to leading seminars and workshops internationally. His books include The Nonresidential Missionary (MARC, 1990), Something New Under the Sun (IMB, 1998), the booklet Church Planting Movements (IMB, 2000), The Camel Workshop: A Practical Guide to Muslim Evangelism (WIGTake Resources, 2009), and Church Planting Movements: How God Is Redeeming a Lost World (WIGTake Resources, 2004). Dr. Garrison currently lives with his wife of 30 years, Sonia, and two of their four children in Colorado where he serves as the International Mission Board’s Global Strategist for Evangelical Advance.

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