Their magic tree house takes Jack and Annie back to the Wild West, where they experience excitement and danger and try to solve a riddle.

When Professor Pepper gives Opie tickets to a ghost-raising instead of a nickel in payment for being guided through the dense fog, Opie manages to make money anyway by helping to thwart a bank robbery.

Introduces Meriwether Lewis and William Clark who, during their exploration of the West for Thomas Jefferson, captured a prairie dog and sent it to the President as a gift.