Ian Stewart has amassed an extremely diverse collection here, with topics ranging from bad jokes ("Q: What's a polar bear? A: A Cartesian bear after a change of coordinates.") to biographical snippets (especially about forgetful mathematicians, like the one who failed to recognize his own daughter) to math-based puzzles to discussions of advanced topics like topology and some advanced number theory.
For the high school student, much of the material in the book will probably be hard going, but the great thing about the book is that it is so full of fascinating problems and diversions that it is necessary only to turn a page or two to get to something more congenial to the reader. For the more advanced college math major, there is much here to educate and delight.
To give but a single example of the mathematical puzzles the book deals with, I will refer to Professor Stewart's treatment of the sequence "1, 11, 21, 1211, 111221, . . ." In this sequence each term after the first is constructed by "reading" the previous term. Thus, the fourth term reads "one 1, one 2, two 1s" and thus generates the fifth term. At first glance, there seems to be little mathematical about this sequence. It's more of a cute brain teaser that really has little to do with math. But what if we asked how many digits the nth term has? Professor Stewart presents that response and an approximation. (In this case, he does not explain the derivation of the approximation, but the point is that he does go well beyond the standard treatment of the sequence.)