THE LAST EMPRESS: The Life and Times of Alexandra Feodorovna by Greg King (Birch Lane: $24.95; 430 pp.) It is a telling detail, a portent, if you will. Little Princess Alex of Hesse, summering with Queen Victoria at Buckingham Palace, is fascinated by one of Grandma's mechanical toys, a full-sized lion with a crank for a tail. "When the tail was turned, the lion opened his mouth and swallowed the model of a Russian soldier." Swallow Russia she did, the girl who grew up to be Alexandra, though hardly single-handed and not by design. It is a familiar story: Nicholas rules Russia; Alexandra rules Nicholas; Rasputin rules Alexandra. Everyone is slaughtered--except maybe daughter Anastasia--and Russia lives unhappily ever after. A familiar story but one that hasn't begun to lose its quota of captivation. Handsome, feckless sovereign; fey, haughty Anglo-German who hitches her wagon to a czar; hemophiliac heir; sex-crazed mad monk--can't miss. Nor is King's entry any less fascinating than its predecessors.