More Adventures of the Great Brain, by John D. Fitzgerald, was published in 1969 by Puffin.
Has Tom Fitzgerald, 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, even convicing the whole town there’s a prehistoric monster on the loose. The citizens of Adenville, Utah, can count on the Great Brain’s genius, from finding the ghost of Silverlode to helping Britches Dotty act like a lady. Then someone robs the bank, and even the police are stumped. Can the Great Brain solve the crime and put the crooks behind bars?