Nate the Great investigates the mysterious disappearance of the purple plastic octopus that his baseball team uses for second base.

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.

Jasmine has looked forward to spending Girls Day with her family and best friend, Linnie, but first her sister says she will not participate, and then Jasmine upsets Linnie.

Nate the Great interrupts his backyard vacation to find his friend's lost grocery list--before lunch.