The Aldens are visiting friends for a big Dia de los Muertos celebration. The kids love learning about the holiday and helping out - that is until mysterious events threaten to ruin everyone's preparations. Can the Aldens figure out what's going on and help their friends save the celebration?

While spending two days touring a zoo to see the baby animals, the four Alden children, aged six to fourteen, help catch an escaped monkey, participate in a photography contest, and investigate a missing camera.

While helping their grandfather prepare for Greenfield's Winter Festival, the Alden children uncover a mystery surrounding the statue in the town square.

While exploring the caves around Dragon's Mouth Cavern, a series of unusual and somewhat frightening events convinces the Alden children that someone does not want them around.

The Aldens investigate when a new store called the Game Spot opens in town and the neighboring shops are robbed.

The four Alden children, aged six to fourteen, volunteer at the new recycling center in town, and help uncover who is breaking in and making a mess each night.

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.

Someone is trying to put Aunt Jane's motel out of business, but the Alden children aren't going to let that happen.

The Aldens investigate when exotic and endangered animals begin to disappear from the zoo where their new friend Lindsey works.

When popular Lizzie Lovett goes missing, seventeen-year-old Hawthorne, a lonely misfit, finds herself becoming obsessed with solving the mystery. Bad things don't happen to popular girls like Lizzie Lovett-- until her disappearance became the one fascinating mystery the sleepy town of Griffin Mills has ever had. Hawthorn is convinced she'll turn up at any moment, and comes up with her own theory for Lizzie's disappearance. A theory way too absurd...