The story started with an office party. A man had to sit on a high open window ledge and drink a bottle alcohol/beer. Falling out of the window and hitting the pavement, the man, obviously dead, starts to ask the question why all these people looking on aren't doing anything to help him. The story then goes with the man as he travels through hell and purgatory and out the other end into reincarnation.
However, the main character is still in hell at the end of the novel. Apparently he gets out in the 2009 sequel Escape from Hell which I haven't read.
Plot summary from Wikipedia:
Inferno is based upon the hell described in Dante's Inferno. However, it adds a modern twist to the story. The story is told in the first person by Allen Carpentier (né Carpenter), an agnostic science fiction writer who died in a failed attempt to entertain his fans at a Science fiction convention party. He is only released, after many decades, from a Djinn-bottle in the Vestibule on the outer edge to Hell when he finally calls upon God for mercy. Upon release he is met by Benito, or Benny, a Virgil-like figure whose full identity is not immediately apparent. Benito offers to take him out of Hell by bringing him to the center.
At first, as Allen and Benito travel through Hell, Allen tries to scientifically rationalize everything he sees, renaming his surroundings as 'Infernoland', a high-tech amusement park some thousand years in the future. It isn't until he sees a man recover from incineration and his own leg heal from a compound fracture that he starts to actually believe that he is in Hell. From this point on, as Allen travels through the inner circles of Hell, he sees how he is guilty of each of the sins in some fashion, commenting to himself that he is in no danger from ditch 3 of circle 8 (simony) only because he has never had any holy offices to sell. At first Allen views the punishments for these sins as far surpassing the crime, repeatedly thinking, "We're in the hands of infinite power and infinite sadism", although he comes more and more to accept the justice of the situation as he realizes that it is their continuing denial of their sins that keeps many of the condemned in hell. Eventually Allen takes over Benito's role in helping reformed souls proceed onto Paradise via Purgatory, allowing Benito to move on towards Purgatory himself. It is revealed that Benito is actually Benito Mussolini, the former dictator of Italy.
Along the way Allen meets a number of his Californian acquaintances and notable people from history (e.g. Epictetus, Billy the Kid, Jesse James, Bob Ford, L Ron Hubbard, Henry VIII of England, Vlad Tepes, Aimee Semple McPherson, William M. Tweed, Al Capone) and from classical mythology (e.g. Hector, Aeneas, Charon, Minos, Phlegyas, Geryon). Due to the long time he spent bottled up in the outer vestibule he also meets some people from the future of 1976, such as a space shuttle pilot.