To Linda Cashdan of The Word Process, for her editorial guidance early in “the process.” Thanks again for your input. To Erika Lease, M.D., for her invaluable contribution on the medical side of things. To Carol Fitzgerald and everyone at bookreporter.com, for designing and maintaining my Web site. To Connie Asero and everyone who participated in the Crystal Coast Book Festival. It was an extraordinary event. Thanks for letting me be part of it.

Thanks to everyone at Kensington, especially Steven Zacharius, Robin E. Cook, Laurie Parkin, Maureen Cuddy, Michaela Hamilton, and Doug Mendini, a true fixture on the trade show circuit. To Meryl Earl, who has somehow managed to get my books published in a multitude of languages, none of which I understand. To Rosemary Silva, for her outstanding work with the copyediting. Also thanks to Alex Clarke and the entire team at Penguin Books for their continued support in Australia and the U.K.

To my editor, Audrey LaFehr, for her enthusiasm, encouragement, and exceptional patience. Thanks for everything. To my agent, Nancy Coffey, for many, many things. If I had to name them all, the acknowledgments would be longer than the book itself. So thanks for all that you do. Let’s hope this is just the third of many. And to Dezzy Murphy and the other Irish climbers who conquered Concordia, thanks for inspiring the prologue.An “invisible” is CIA-speak for the ultimate intelligence nightmare: a terrorist who is an ethnic native of the target country and who can cross its borders unchecked, move around the country unques- tioned, and go completely unnoticed while setting up the foundation for monstrous harm.

THE KARAKORAM HIGHWAY (KKH), PAKISTAN

In Rebeka Cˇesnik’s opinion, the view, even when seen through the cracked window of the ancient bus winding its way down from Kashgar to Islamabad, was simply magnificent. Perfect. Stunning in every conceivable way. These were the words she had used to describe every trip she’d ever taken, and her effusive comments always made her friends and relatives smile, though it had taken her quite a while—the better part of her life, in fact—to understand just why that was.