Esther B. Robinson’s fascinating biography opens, a little misleadingly, with a phone message from a one-time habitué of Andy Warhol’s Factory who claims not to remember Danny Williams, the director’s uncle. Yet Robinson got interviews with nearly every relevant Factory veteran who’s still breathing, including John Cale, Chuck Wein, Brigid Berlin, Danny Fields, Billy Name, and Paul Morrissey, who vaguely admits to getting into a fistfight with Williams at a Velvet Underground gig in Chicago. (About sex? Drugs? No, electrical cables.) The movie tells three roughly parallel stories: Williams’ disappearance in 1966 while visiting his family in Massachusetts; his relationship, perhaps sexual, with the emotionally remote Warhol; and the posthumous discovery within Warhol’s cinematic archive of Williams’ distinctive and previously unknown films. Clips from those shorts are interspersed with contemporary interviews and archival footage, offering yet another vantage point on the much-documented yet still elusive Factory. Robinson recovers much of her uncle’s short and largely forgotten life, including his editing work for the Maylses brothers, yet Williams retains enough mystery to qualify as an exemplary Warhol acolyte.