The narrator of The Tunnel is a distinguished man in his fifties, William Frederick Kohler, a professor at a Midwestern university. His principal subject, the Third Reich. He has just completed his massive magnum opus, Guilt and Innocence in Hitler's Germany.

All that remains to write is an introduction. Kohler sits down to write a self-congratulatory text and finds himself unaccountably blocked. He begins instead to write an entirely other book, another history - that of the historian himself. What he writes is the complete opposite of his clearly argued, causally determined history of the Reich. It is as subjective and private as history is objective and public, as apparently shapeless and stagnant as history is ordered and directive.

It is chaotic, obscure, full of lies and disguises, gaps and repetitions. Indeed, his Introduction is so personal that he fears his wife will find it, and he slides the manuscript between pages of his book, where he knows it will not be found. At the same time, Kohler begins digging a tunnel out from the basement of his house.

The tunnel comes to mirror Kohler's digging into his life - his feelings, his past, his own few loves and many hatreds. The writing, the digging, the reader's reading, continue together, creating a hole driven into both language and the past, getting closer to and fleeing from the secrets of the novel's fundamental theme - the fascism of the heart.