The Great Brain is Back, by John D. Fitzgerald, was published in 1995 by Dial.
Tom D. Fitzgerald—better known as The Great Brain—has turned thirteen, and pretty Polly Reagan has put a spell on him. But when it comes to swindling his younger brother J. D. and all the other kids in Adenville, Utah, Tom hasn’t changed a bit. From thinking up the slippery soap deal and the numbers game to outwitting a band of murderous outlaws, The Great Brain is at the top of his form. And one thing’s for sure: life is more exciting when he’s around!