Gertrude Chandler Warner
The zoo is wonderful - it has seals and giraffes and elephants and tigers, and Benny's favorite, a little monkey named Amos. It also has a mystery. Someone is mixing up signs, switching off electricity, and endangering the animals' lives. If the Boxcar Children want to save the animals, they'll have to solve the mystery - and fast!
At the beach, Benny finds a valuable gold locket and decides to try to find its owner. Soon the children are caught up in a puzzle involving strange visitors at the beach and the mysterious Miss Smith,...
Henry, Jessie, Violet, and Benny once lived on their own in a boxcar... The Boxcar Children are spending the summer in a tiny, quiet New England fishing village. The little schoolhouse doesn't have a proper teacher, so the Aldens are teaching! There's also a very old library where nobody ever goes — nobody, that is, except for a mysterious stranger. For such a small town, Port Elizabeth has a lot of secrets! Look for more Boxcar Children
...14) Caboose mystery
When their friend Sam gets a letter full of riddles from an eccentric millionaire, the Aldens are eager to help him crack the code. If Sam can solve the puzzle, he will inherit the millionaire's money! But Sam isn't the only one in town to receive a letter - and whoever solves the mystery first will win the prize!