The three eleven-year-old sleuths watch as a new wildlife bridge is being built across two freeways in Southern California so animals can roam where they always did. Too many of them are trying to cross and are getting hit by cars and trucks. The three discover that poachers are taking advantage of the bridge that funnels the wildlife across-deer, bears, feral horses. How to stop them?

Suggest reading the series in order:

1 The Mystery at the Stables

2 The Mystery at the Rodeo Ranch

3 The Mystery of the Silver Saddle

4 The Mystery at the Horse Auction

5 The Mystery of Sable Islan

6 The Mystery at the Pony Baseball Game

7 The Mystery at the Wildlife Crossing