HELLMAN AND HAMMETT The Legendary Passion of Lily and Dash By Joan Mellen HarperCollins: 549 pp., $32

The three-decade relationship between Dashiell Hammett and Lillian Hellman ranks with Scott and Zelda and Jean Paul Sartre and Simone DeBeauvoir in 20th century literary legend. But while the others merited individual biographies or studies, Joan Mellen makes it clear that the stories of Dash and Lily can’t be separated: Hammett’s career as a writer was nearly over by the time he met Hellman in 1930, which is where the literary portion of Hellman’s career and the interesting part of Hammett’s life begin.

“Hellman and Hammett” is skimpy on the early part of Hammett’s life and the events that led up to the writing of his classics, “Red Harvest,” “The Maltese Falcon” and “The Glass Key.” But Mellen’s book is definitive if only because it gives us an enormous amount of information on what we haven’t been told about Hammett before, largely because Hellman succeeded in keeping it from us.

It’s the first book about either one written after getting free access to Hellman’s papers--in other words, the first book on either one that Hellman couldn’t control. The result would appear to support Mary McCarthy’s famous remark about Hellman: “Every word she writes is a lie, including ‘a’ and ‘the.’ ”