Suppose the family cat were left behind at a beach cottage? Because, save for one wrinkle, Siamese cat Fritzi's experiences and reactions are not only plausible but lifelike, the question can fairly be put as a come-on. Left on Fire Island by the Arnolds after she inadvertently disappears, Fritzi is prey to dogs and foxes (and once, almost captured), and herself feeds on mice and rabbits--as well as learning to seize gulls' catches, to scour the beach for mussels and clams. A gray cat, first seen as a threat, becomes Fritzi's mentor and, briefly, her companion; the snow proves valuable too, ""not only as a source of water, but as a recorder of island life."" And Fritzi has already survived the worst of the winter when she comes upon a lone shack inhabited by a temporary recluse (with more fictional than real-life equivalents) who gives her two-months shelter. But when he departs, Fritzi resumes her stalking without emotional pangs--and author Chambers even leaves in doubt the extent to which she's still thinking of the Arnolds when they return in the spring. There's no question of their joy, though, at the eventual reunion. This is one book, indeed, in which the humans come off as well as the animals--one misguided soul turns up, but there's not a wretch in sight. (On the other hand, it's good to see a domestic animal being independent.) Written with more than average polish and descriptive skill, it may also be for the more than usually attentive child, content to settle in without dramatic pyrotechnics.