During an archeological dig on an ancient ruin, Cornelius uncovers an ancient, human-made book entitled 'A Day at the Zoo'. Needless to say, the images and words inside could lead to much trouble for man and ape alike....

Bill, Jeff and Judy are heading for the human settlement across the plain between the mountain ranges when they spy human shapes far below. Are they about to encounter more free humans or individuals that are dangerous to all three?