Book 1

Two sets of twins suspect their neighbors of wrong-doing when they observe the strange behavior of the couple's nephew.

Book 2

Two sets of twins receive a message in a fortune cookie, warning them to beware of a man in a blue hat.

Book 4

Two sets of twins catch a thief while tracking down a missing suitcase in a train station.

When a famous sculpture is stolen from the museum, two sets of twins team up to track down the thief.

Bo teaches his dog Dolby some unusual tricks in an attempt to win the Woof-Off contest.

In an extraordinary day at the beach, after winning a sand castle contest, two sets of twins resolve the mystery of the disappearance of a rich woman's dog.