The best con man in the Midwest is only ten years old. Tom, a.k.a., the Great Brain, is a silver-tongued genius with a knack for turning a profit. When the Jenkins boys get lost in Skeleton Cave, the Great Brain saves the day. Whether it's saving the kids at school, or helping out Peg-leg Andy, or Basil, the new kid at school, the Great Brain always manages to come out on top-and line his pockets in the process.

Tom a.k.a. the Great Brain, is off to boarding school. Now his little brother, J.D., is free to follow in Tom's ingenious, conniving, and profitable footsteps. All of J.D.'s attempts at turning a profit fail miserably, and he soon realizes that he just doesn't have that crafty Great Brain knack. But when his younger brother is kidnapped, J.D. finds that his little brain may not be so ordinary after all . . .

Has Tom, a.k.a. the Great Brain, given up his con-artist ways for a bicycle? Not for long. Soon the Great Brain is back to his old tricks, swindling and trading, and even convincing the whole town there's a prehistoric monster on the loose. But when someone robs the bank, even the police are stumped. Can the Great Brain solve the crime and put the crooks behind bars?