The first part of their vacation aboard a houseboat puts the Timberlines up close and personal with a celebrity couple. Bryce and Ashley get to see real-life paparazzi in action while they work to solve a mysterious break-in on the celebrity boat. But the lazy days on the river didn't prepare them for the deadly challenges of the Grand Canyon hike.

Bryce and Ashley Timberline are normal 13-year-old twins, except for one thing—they discover action-packed mystery wherever they go. Wanting to get to the bottom of any mystery, these twins find themselves on a nonstop search for truth.