Henry, Jessie, Benny, and Violet Alden meet Mike Wood and a strange chain of events begins. Mike's house is mysteriously burned down, a man in a blue hat appears, and the Aldens' uranium mine is in danger of being sabotaged.
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.
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.
"Jessie and Henry's robotics team is competing in a big tournament. But when their robot is stolen, the Aldens have a high-tech mystery to decode!"--Back cover.
"The Aldens are helping out at a doughnut shop, but when a rival store opens across town, strange events follow, and the children have a mouthwatering mystery to solve!"--OCLC.
"When the Alden siblings visit their grandfather's friend in an apartment building, they begin to wonder about the many mysterious events that keep happening on the thirteenth floor of that building" OCLC.
Henry, Jessie, Benny, and Violet Alden meet Mike Wood and a strange chain of events begins. Mike's house is mysteriously burned down, a man in a blue hat appears, and the Aldens' uranium mine is in danger of being sabotaged.
"The Aldens are helping out at a harvest festival in a town at the foot of the Rocky Mountains. But something in the hills is scaring people away! Are the local rumors about a werewolf true?"--Back cover.
