The robbery of the treasure in the tower proves to be an exciting challenge to Frank and Joe. Frank and Joe attempt to foil a ruthless espionage ring in their effort to sabotage the United States space program.

When a sinkhole opens up and swallows one of Bayport?s historic statues, Frank and Joe suspect something?or someone?shady at play. They jump at the chance to investigate; Joe as a member of an urban exploration club, and Frank as photographer for the school paper. But in the thick of their search, the boys stumble upon an entire underground city that?s been abandoned for years. Now the city is home to a cultish band of criminals who plan to take over...

While on a school trip to the British Arts & Antiquities Museum, John Watson and his friends from the Baker Street Academy get involved in a mystery when the Alpine Star, a famous diamond, is stolen.

After Minty discovers a secret tree with a hollow trunk that holds the secrets of everyone in the neighborhood, Raymond, a new boy drawn to the tree and Minty start watching their neighbors.

When the daughter of Bayport's amusement park owner goes missing, Joe and Frank follow clues to find the girl and determine if her disappearance is related to that of another missing person.

When his cousin is captured by the king of the dragons, Geronimo must deliver the Crown of the Seven Rubies to free him.

When one of the helmets in Sven the Shouter's private collection is stolen, the micekings find their investigation complicated when the dragons attack.

"Nancy investigates her father's disappearance in Washington, D.C. in the twenty-second book of the Nancy Drew Diaries"--

While vacationing at Skull Castle, Geronimo encounters a ghost cat that is threatening the special pumpkins that grow in the Von Cacklefurs' garden, and it's up to him to find out who wants to steal the pumpkins.

As Winnie attempts to solve a mystery surrounding a circus horse, she struggles to keep a "normal" family life despite the absence of her mother.