The Secret of the Ancient Astronauts by Christopher Workman
This book continues in the tradition of "The Three Investigators." Naturally, the story begins at the Jones' Salvage Yard, where the three boys can often be found at Investigators HQ (an old mobile home, hidden in the yard.)
The family pickup truck, fresh from a collectible buying hunt, returns after nearly being run off the road. There's nothing too interesting in this latest batch of junk--or is there? There are some mysterious statues, and Jupiter Jones is quick to investigate. He was especially interested in "what was sandwiched between a mattress and the dresser: the broken remnants of a stone statue."
There were a trio of little figures, which were facing another figure in the middle. That middle figure was especially strange. It had a "box-like helmet wrapped around its entire skull, leaving only the face visible." That wasn't all. This figure had something curious on its throat:
"Upon closer inspection, Jupiter noted its resemblance to a mouthpiece. Yet the apparent antiquity of the statue suggested that the figure had been carved before such technology had been invented."
And just like that, the Three Investigators find themselves deep in a strange mystery. Jupiter quickly calls in his friends: "Red Gate Rover, Door Four, 1500 hours. We’ve got a case!”
Don't miss all the chapters in this adventure of The Three Investigators. The entire book is available for free download from threeinvestigatorsbooks.
