A whole book about sea turtles? Yes, and like Rudloe's previous performances (The Sea Brings Forth, The Living Dock at Panacea), it's a consistently engrossing shell game. Leatherbacks, on a diet of jellyfish, are the largest, ridleys the most mysterious, hawksbills the source of tortoiseshell, greens a favorite of gourmets. Most species are endangered (which occasionally pits conservationist Rudloe against his Florida fishing industry neighbors) but turtle-watchers are tagging more each year, and their observations have confirmed much that was merely speculative--where ridleys nest or what green turtles do during non-breeding years. As before, Rudloe moves his markers expertly, offering a characteristically smooth blend of biology, personal anecdote, and folklore (a terrapin hex, the Turtle Mother myth). He witnesses a 1000-pound Surinam leatherback lay eggs in the darkness; enjoys--without remorse--fresh (illegal) turtle soup; and, in classic form, eventually stumbles on a turtle-head rock with a magnetic snout: it just may hold a key to the puzzle of how turtles orient. A deftly introduced, artfully paced look beneath the carapace.