The twelve-year-old twins John and Abigail Templeton are both clever, pragmatic, theoretical, and cryptic. Their father is sort of a brilliant scientist, and because of that the adult twins Dean D. Dean and Dan D. Dean kidnap John and Abigail to hold them for ransom in order to get one of Mr. Templeton's inventions. The twins use their brains and eventually figure things out.
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Professor Templeton has been hired by the Thespian Academy of the Performing Arts and Sciences to invent something, anything, important (and profitable) but the thirteen-year-old twins, Abigail and John, are suspicious and determined to investigate.