Henry, Jessie, Violet and Benny no longer have to live in an abandoned boxcar. They've found a new home with their grandfather. And when school's out for the summer, the kids get to spend vacation on their grandfather's private island.

The Aldens visit an old camp in Quebec, Canada, and begin to suspect that someone or something is trying to scare them away from the place.

When their favorite author fails to arrive as scheduled to speak at the local library, the Alden children investigate how he could board a train and never be seen again.

Benny wants to get something special for his grandfather's birthday, but he has trouble finding the right present while trying to keep an eye on his dog Watch.

Benny anticipates making friends with the new kid down the street, but when he finds out that she's a girl, he is very disappointed.

When the Aldens help a friend of their grandfather's to build the world's largest yo-yo, they soon discover that more than one person is trying to prevent them from finishing the job--and for more than one reason.

While helping out part time in a pet shop, the Alden children discover an employee who is smuggling and selling exotic animals.

The Aldens visit Grandfather's friend at the Ogopogo Retreat and aided by puzzling clues, embark on a treasure hunt to prevent the retreat from being sold.

"One day in the park, the Aldens' dog, Watch, comes across a mysterious box with a note inside. 'Congratulations!' the note says. 'You've found it!' The box is part of a game called Geocaching. Soon, Henry, Jessie, Violet, and Benny are searching all over town for hidden boxes and making friends with other kids in the geocaching club. But is one of the club members a thief?" -- p. [4] of cover.