The Aldens' dog, Watch, comes across a mysterious box with a note inside, a box that is part of a game called Geocaching. Henry, Jessie, Violet, and Benny join the game but soon suspect one of the members of the geocaching club is a thief.

The adventures of the four Alden children as they spend a summer vacation on their very own island, purchased by Grandfather's father years ago.

While visiting Lake Lucille in the Adirondack Mountains, the Aldens hear stories about a monster in the lake and then encounter evidence that it may be real.

When the Alden children go camping on Blizzard Mountain, a place said to be inhabited by a ghost looking for buried treasure, they begin to think someone or something is trying to scare them off.

While in New Orleans helping mystery writer Olivia Chase open a new bookstore, the Boxcar Children investigate the mystery of some disappearing books and uncover some valuable items

Because they do not want to be separated, four orphaned children run away and live in an old abandoned boxcar