In number 16 in this popular series, D.W. volunteers her big brother's services taking care of the rambunctious twins visiting their grandmother, Mrs. Tibble, in her dauntingly huge Victorian house. Mother and Father are sure Arthur will rise to the occasion, and so he does. After the obligatory tough start, he gets the twins' number: when they hide, he remarks: ``I sure hope I find them before the swamp thing does!'' Out they pop, ready to cuddle up for scary additions to his impromptu story. Cozily predictable, with plenty of amusing dialogue and comical pictorial details. (Picture book. 4-8)