Intrigued by legends and romance, journalist Dea Birkett gets herself to three-square-mile Pitcairn Island for a sojourn among the descendents of Captain Bligh's mutinous crew. Interweaving history and observation, Birkett has written a fascinating account of the island and its isolated population (who didn't like her much or appeciate a journalist in their midst).  (PAC28, $17.00)