Allen Carpenter, a science fiction author, dies in a stupid stunt at a scifi convention and finds himself in the vestibule of Hell – as described by Dante. Like Dante, Allen has an Italian guide through Hell, traversing all circles in an attempt to escape. Just as Dante met an amazing number of his own contemporaries in his travels, Allen runs into many he knew in life. As Allen goes lower and lower into Hell, he finds it is exactly as Dante had described.
Pournelle and Niven have updated the sins for a "modern" era (food faddists in the glutton's level, diehard industrialists and environmentalists battling each other in Hell, a dig at L. Ron Hubbard for starting a false religion and another dig at Vonnegut for his vacuity).