The disappearing staircase mystery: When the Alden children join a group of volunteers to fix up an old house for senior citizens, they try to explain the puzzling behavior of their coworkers as well as investigate some unusual events.
The mystery on Blizzard Mountain: 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 mystery of the spider's clue: 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.
Contents
The disappearing staircase mystery -- The mystery on Blizzard Mountain -- The mystery of the spider's clue.
