When a professional hockey player comes to Greenfield with plans to build an ice skating rink, the Alden children suspect that someone in town wants to stop the project.

Henry, Jessie, Violet, and Benny--four children who used to live alone in a boxcar and now reside with their grandfather--arrive at Camp Seagull overflowing with excitement, but they soon realize that some of the other campers are not above cheating in the annual camp Olympics.

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.

The Aldens try to find the thief who stole a very rare teddy bear from the toy hospital at the teddy bear festival.

The Aldens accompany their grandfather to his class reunion and investigate the possibility of a buried Civil War treasure, and of a ghost in the bell tower, at Goldwin University.

While vacationing at a friend's country home, the four Alden siblings try to find a long-missing, priceless brooch, while also investigating the existence of a ghostly stream.

When an elderly friend is injured, the Alden children offer to help him with his window-washing business in their small town of Greenfield and agree to help him solve a riddle that has arrived in a mysterious invitation.

Henry, Jessie, Violet, and Benny begin to dig into the past of the old boxcar turned playhouse in their back yard and discover clues about why it is being haunted.

The Alden children are helping grow vegetables in a restaurant owner's garden, but when the tomato plants are moved from their original position the children begin to suspect that the move is connected to a robbery at the local bank.

The four Alden children, aged six to fourteen, uncover a mystery while volunteering at a food pantry for the needy.