The daughter of romantic idol John Gilbert offers a sympathetic, fairly candid, but not-very-probing biography--which more or less blames his downfall on a conspiracy of sabotage masterminded by MGM's Louis B. Mayer. (It's a familiar theory--on view in Garson Kanin's trashy novel Moviola, in recent Mayer bios, and elsewhere.) Drawing, perhaps too uncritically, on her father's memoirs, Fountain sketches in Gilbert's early years: his ""spirit-crushing childhood"" with no father and a self-centered mother (a touring actress who frequently abandoned the boy); his storybook climb from teenage poverty to beginnings, as a gawky extra, in the silents (""If there was a heaven, Jack felt, it couldn't be more thrilling than this""); his rocky marriage to Fountain's mother, actress Leatrice Joy, who was the bigger draw at the start. Then comes Gilbert's mid-1920s burst of superstardom--from Elinor Glyn's His Hour through The Merry Widow, The Big Parade, Flesh and the Devil, and Love. The last two co-starred Greta Garbo, of course: ""by the time their first love scene was filmed they were madly, exuberantly in love."" But though ""Garbo loved him as much as Garbo was capable of loving,"" she refused to be ""possessed,"" left him standing at the church, toyed with him. (By later marrying Ina Claire, however, ""Jack was probably the only man in her life who ever walked out on"" Garbo.) Meanwhile, too, Jack's career began to decline, despite his own keen efforts to avoid ""Great Lover"" stereotype roles: the sound-track of the notorious talkie His Glorious Night may have been doctored to make Gilbert's voice seem higher; in any case, there wasn't any scornful audience response to his quite passable voice--until the press began a campaign against him (on MGM orders?); he was given no more good roles; Mayer's ""unrelenting hatred""--because of a rough fight between them--was apparently behind it all. And, despite a frail comeback in Queen Christina and the mothering of ""magnificent"" Marlene Dietrich, Gilbert became depressed, increasingly alcoholic (""the Scotch seemed to help keep away the night""), and mortally ill, dying from heart disease at 36. While not omitting the boozing and womanizing, Fountain definitely sees her father (who died when she was eleven) in not-always-convincing soft focus: a naif, a victim, a serious film-artist, an ""uncomplicated, nice-guy romantic."" And there's no substantial ""untold story"" here--especially since Garbo's still not talking. But, with first-person testimony from many Tinseltown old-timers (including Fountain's mother) and the author's own strong involvement, this is a few cuts above the standard celebrity-pasteup--strong on warmth and nostalgia.