The Story of Mrs. Robert Louis Stevenson exhaustively researched (with some newly released material) and expansively retold (some 600 pages) is inevitably, in tandem, that of Fanny Stevenson's more famous husband whom she married when he almost died and had written his Requiem. ""A romance of destiny"" which was to become ""more a symbiosis than a marriage"" (another biographer), their relationship has puzzled many since just as it antagonized others in their day. Mrs. Mackay really never makes it come alive--perhaps it never did--and to some extent one remembers here the chronic, pathetic facts of their existence (his tuberculosis; her depressions; debts; etc.) which to a degree swaddles Robert and his Fanny--that intuitive, headstrong ""tiger lily beauty"" whom Henry James called a ""poor, barbarous and merely instinctive lady."" Mrs. Mackay has told the entire story from her childhood and her first marriage to an attractive philanderer through to her last twenty years as Stevenson's widow, when the legend surrounding them both occasioned a great deal of critical speculation. Granted time, and the interest in the Stevensons to bear with a certain amount of unselective external detail, she has told their story in a fair, agreeable and unexacting fashion.