After 30 years of labor, Gass (Habitations of the Word, 1984, etc.) has brought forth a big, big book that sets off, with linguistic and intellectual bravura, to explore the dark corners of history and the psyche. But it never quite reaches its destination. William Kohler, a noted historian, has recently completed his ``Great Work''--The Guilt and Innocence of Hitler's Germany. All that remains to be written is the introduction, and yet as he sits in his chair he finds himself writing a personal history of life spent mostly in a chair: ``a domestic epic that took place entirely in the mind.'' Drawings, typographical whimsies, and scabrous limericks frequently interrupt this often dense text, which, like a drop of water seen under a microscope, teems with rich and intriguing life. As Kohler writes, he hides the pages from his wife within those of his official manuscript. And he also begins to dig a tunnel from his cellar, a place for ``concealment of history beneath my exposition of it.'' An aphorist, Kohler delivers the mots--bon and juste--at the speed of a stand-up comic, but their wit and insight conceal a sickness of the soul. Most people, including himself, Kohler asserts, belong to the ``Party of the Disappointed People,'' people who recognize ``that the loss has been caused in great part by others.'' Preoccupied with evil, the nature of truth, and the effects of an individual's relationship with others, he recalls his bookish childhood with a mother who drank to remember the ``good old days'' and a bigoted father; graduate work in prewar Germany, where he hurled a brick on Kristallnacht; his unhappy marriage; and the lost love of his life, Lou, a former student. Kohler's story exhibits the same inconsistencies and deceits he finds in history: Kohler, the personal memoirist, is, it seems, as unreliable as Kohler, the eminent historian. A virtuoso performance without a grand finale. But what a remarkable show.