The octopus turns up in Kris and Maxi Hart's bathtub because their biologist father thinks it will inspire him to write stories for children while home on sabbatical. Daddy finds it's hard to write for children (so there!)--but creative fifth-grader Kris, who doesn't even want the octopus, fills her journal with fanciful versions of fairy tales featuring Octo-Puss in Boots and Octarella. Terris supplements these with mangled nursery rhymes, at the top of every chapter, about octopus pie or stew or soup. Then comic-book-reading John Dorfman (""Doff"") gets into the act with his ""Octopus-Man,"" and Kris realizes that he is ""not stupid, just enthusiastic and imaginative""--even though he isn't, like the Hart girls, in the GATE (Gifted and Talented) class that big-word-using (and misusing) Mari maintains divides the smart kids from the stupid. (Gram, who's the school media specialist, thinks otherwise and champions Dorf.) Sixth-grader Mari, for her part, has welcomed the octopus and talked Daddy into letting her take it to school; she hopes it will win her attention and, with it, a boyfriend. Then the octopus is octnapped from the school media center. A mystery, at last! Mari and Kris suspect Doff, Doff and Kris suspect Mari--but it is non-stupid Doff who first recognizes the real culprit, communicating his ""clues"" to Kris in his ""Octopus-Man"" story. Non-stupid readers will have guessed already from a reference to the fishy smell in Gram's car. So: the octopus ends up back in the sea; it's Kris who ends up with a boyfriend (Doff); and, in the process, Kris also becomes independent of bossy Mari, to whom she had been in thrall--as Tetris has thumpingly hammered in from the start, perhaps in an attempt to give this whipped-up tempest-in-a-fishtank some psychological ballast. But the interpersonal developments are as mechanically contrived as the silly mock mystery.