Gus, Cora the cat, a mouse named Mouse, and Mr. Frizzle all live in the Historical Museum. They have a fairly symbiotic relationship, until the arrival of this baby ghost that is left on the doorstep. Frizzle who has a terrible temper and is reminiscent of most bad-tempered excessively rigid old men overreacts a number of times in most theatrical and entertaining ways before the mild-mannered Gus stands his ground, puts Frizzle in his place, and restores order to the emotional state of the household.