When their grandfather arranges for them to spend two weeks at Sunny Oaks, the four Alden children enjoy settling into the routines of farm life but become suspicious about a mysterious horse locked in the stables.
At the request of their distant relative Althea, the Boxcar Children arrive at her old Virginia mansion and investigate the mysterious incidents happening there.
Henry, Jessie, Violet, and Benny discover that some of the clues to the Great Detective Race are fake and set out to find out who is trying to ruin the race-- and why.
The children, snowbound in a vacation cabin, discover adventure in surrounding wild life, three children they find in the snow, and a search for a lost recipe.
The Alden children travel on a Mississippi paddle-wheel steamer to visit an old family friend in his cabin near Hannibal, Missouri, and try to discover who is responsible for the mysterious activities near the house.
The Alden children investigate various mix-ups at a zoo run by their grandfather's friend in an effort to save it not only from pranksters but also from the town council.
Henry, Jessie, Violet, and Benny are excited to learn more about raptors when they volunteer at a rehab center for wild birds, but not long after they arrive, a series of strange events makes it seem like someone might be trying to sabotage the center.
While on a camping trip with their grandfather, the Alden children try to find out about the loud music and missing food that threatens to scare away other campers.