Sam Steele and his Junior Spy Agency are back on assignment after a long summer of solving crimes. Sam's history class assignment leads him to his first clues in search of a priceless Russian treasure that's been smuggled into the U.S. Now he and his agency are pitted against Cash and a gang of bumbling thieves as they race to recover the treasure before it falls into the wrong hands forever.

When Salty tells a story about a lost pirate treasure on the Island of Sodor, Thomas sets out to discover if it is true. Meanwhile, Dennis, a new diesel engine, is playing tricks, and Henry tries to prove he is the strongest engine on the Island of Sodor.

Dora and Boots take preschoolers on an exciting underwater adventure to help save the mermaid's kingdom. Dora travels to the bottom of the ocean and finds a hidden treasure chest on Treasure Island.

When a group of young divers discover the wreckage of a cargo plane at the bottom of the sea, they believe their dream of buried treasure has come true. What they don't realize is that there is also millions of dollars of illegal goods that are in that sunken plane and a group of dangerous criminals are already desperately searching for it. As tensions mount and the friends begin to fight about what to do with their find, others get closer to discovering...

Arthur sets out to save his family's home from real estate developers when his grandfather mysteriously disappears. When he finds his grandfather's ancient clues of a hidden treasure, he unlocks a passageway that leads to a spectacular world with little people who just happen to live beneath his own backyard.