When they take their dog, Watch, for obedience training, the Alden children discover that some of the dogs in the class have vanished and decide to try to solve the mystery of their disappearance.
The Alden children suspect that the other guests are somehow involved when things begin to disappear at the bed and breakfast where they are staying in Washington, D.C.
The Boxcar Children rush to investigate when it appears that someone is trying to rid the Ocean Adventure Park aquarium in Florida of its main attraction--a great white shark.
The Aldens are thrilled to be helping out at Cogwheel Stadium as the Clayton Cogs try to win the pennant, but when the children realize someone has stolen the team's pitching signals and given them to the other team, they set out to find the spy before he ruins the team's chance at victory.
The Aldens are selected to participate in a new game show, and as a camera crew follows them around, they compete with another brother and sister team in search of clues in Philadelphia.
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.
