William St. Clair edited Edward John Trelawny's supposed autobiography, Adventures of a Younger Son, in 1974 and evidently found the subject worth pursuing, because he has now written a full-scale biography. It should be definitive. Trelawny was notorious in his day, and his writings have long been hotly debated, partly for their intrinsic interest, but more because he is an important witness for the last years in the lives of the poets Byron and Shelley--and for their deaths. It matters in the world of literature whether or not Trelawny is to be trusted. Long an admirer of Lord Byron's works, he turned up in Switzerland and Italy and was accepted into the poets' circle partly because of his handsome, swashbuckling person, and partly because of the stories he told so well, of an exotic (Byronic) past in the British Navy and as a deserter from it: as privateer, world voyager, rescuer of maidens in distress, but a man willing to fight to kill, with his bare hands if necessary. Later, with help from Mary Shelley, he wrote ali this down, and the controversy began. It still rages (see Gerson, above). St. Clair is fond of Trelawny, not a naysayer or a nitpicker, but he concludes--as his title suggests--that Trelawny was a compulsive fabulist, one who came to believe in his words because he himself had made them up. ""Trelawny was only able to convince people with his stories because when lie was telling them he was convincing himself. He imagined himself into them."" St. Clair has studied all sorts of evidence: books and manuscripts, and also the caves on the face of Mt. Parnassus where Trelawny fortified himself during Lord Byron's Greek war. His documentation is admirable, lively as well as thorough; his illustrations are absorbing. The book is hard to put down.