The Silver Boulder — Andrea Spalding

Sister and brother sleuths Willow and Rick are back! This time they're searching for a lost boulder full of silver, as big as a truck. Everyone they meet in Kaslo, B.C., seems to have a secret. Why is a young woman spying on them? Where is the other half of the treasure map? And is there really a ghost on the SS Moyie? As they hunt deeper and deeper, the discover disturbing things about the past and try to find a way to help new friends regain what they lost.

The first book in the Adventure.Net series, The Lost Sketch, featured Rick and Willow finding a mysterious picture in a boxcar in Ontario, meeting an art forger, and racing against time to find out if the art was created by one of the Group of Seven.