Hiro Protagonist, freelance hacker and the greatest sword fighter in the Metaverse, teams up with Y.T., a fifteen-year-old female courier, to delve into a mystery that mixes Sumerian myth with virtual reality in a gritty cyberpunk setting. Hiro and Y.T., along with Hiro's old girlfriend Juanita, race to stop a plot masterminded by a religious business monopolist that would brainwash the masses and knock freelance hackers out of commission.

Hiro is a freelance hacker who works as a stringer for the Central Intelligence Corporation in his free time. Hiro uploads information to the CIC database, and if anyone buys the information, Hiro gets paid.

Hiro is introduced to Y.T. literally by accident. Hiro lands his pizza delivery car in a burbclave pool while Y.T. is being pulled behind by her harpoon, or "poon". Y.T. offers to deliver the pizza for Hiro, which saves Hiro's life from the Nova Sicilia organization who owns the pizza company. Y.T. does successfully deliver the pizza, much to the chagrin of the customer, and in the process, Y.T. gets noticed by Uncle Enzo, the head of Nova Sicilia. Y.T. calls up Hiro to help get her out of a jam with the MetaCops, and they then agree on an intelligence partnership, with Hiro splitting the proceeds of any profitable intelligence that Y.T. provides him. When Y.T. and Hiro escape into a Mr. Lee's Greater Hong Kong franchulate, they get to see a Rat Thing, a cybernetic security device that is made from "biological components".

In the Metaverse, a computer generated virtual reality, Hiro's old girlfriend Juanita tells him something big is up, and gives him a library of information. Hiro's friend Da5id is disabled by a virus known as Snow Crash, which was given to Da5id by a man named Raven. The virus was manifested by naked female avatars unrolling scrolls to display a bitmap static image. The virus causes Da5id's avatar to break apart, and Hiro later learns that Da5id was also disabled in real life from the virus.

Hiro begins to delve into the library of information that Juanita gave him, with the help of a program called The Librarian. The data was gathered by a Dr. Emmanuel Lagos. Hiro reviews the data on L. Bob Rife, a billionaire cable-tv baron who has monopolized the fiber optic cable market across the world. Rife seems to be interested in ancient Sumerian myths. Rife also purchased an aircraft carrier and rescued thousands of refugees in Bangladesh. Hundreds of smaller boats are lashed onto the aircraft carrier, and the collection is referred to as "the Raft".

Hiro meets up with Lagos at a Vitaly Chernobyl concert. Lagos is a gargoyle, an intelligence agent that wears computers and other equipment all over his body. Lagos tells Hiro that the Sumerians didn't differentiate between evil and disease, and starts talking about nam-shubs. Hiro thinks Lagos is crazy. Hiro sees Raven deliver a briefcase to a group of Crips. One of the Enforcers providing security at the concert finds Lagos's body, sliced open from crotch to jaw.

Jason Breckinridge, a franchisee for Nova Sicilia, gets a priority delivery to a franchise in Compton where Uncle Enzo will be visiting. Jason decides to deliver the package himself, and gets yelled at because the Mafia wanted Jason to have a Kourier, specifically Y.T., deliver the package, because Uncle Enzo wants to meet her.

Hiro and the Enforcers chase after the Crips, who are going after Raven. The suitcase that Raven gave to T-Bone, the head Crip, blew up. Raven kills two of the Crips with bamboo spears and a glass knife before he escapes. The Enforcers look at the blown up case, and the head Enforcer tells Hiro that the drug that was in it is Snow Crash. The head Enforcer tells Hiro that they are trying to protect Raven because Raven carries a nuke in his side car hooked to "dead man" sensors in his brain.

Jason pays Y.T. a lot of money to deliver the package to the Nova Sicilia franchise in Compton, and even drives ahead of her so she can poon his car. Y.T. delivers the package to Uncle Enzo, and he treats her like an equal, unlike most of her deliveries. Uncle Enzo gives her his dog tags. One of the Mafia Boys gives Y.T. a new job. Y.T. goes to Griffith Park to pick up the package for the job, and all of the people there are babbling nonsense. One of the men gives Y.T. a case like the one she saw blown up the previous night. In transit, Y.T. is intercepted by a Mafia truck carrying Fisheye and some other men, and they scan the case. Y.T. delivers the case to a Reverend Wayne's Pearly Gates franchise where the pastor takes a dose of the Snow Crash drug.

The military comes and picks up Hiro at his storage unit, and they go to see Da5id in the hospital. Da5id is babbling incoherently. Hiro goes to Da5id's house and sees that Da5id's computer has snow crashed.

Juanita explains the background of the Sumerian gods Enki and Asherah to Hiro, and how the bitmap that Da5id had seen was a binary representation of a nam-shub, a neurolinguistic hack. In the Metaverse bar The Black Sun, Hiro cuts the arms off of an avatar who was trying to show Hiro the Snow Crash scroll. Hiro manages to save the scroll and puts it away to examine later. Hiro and The Librarian comb through the data stack for information on the nam-shub of Enki that caused the elimination of the Sumerian language and led to the story of the Tower of Babel. The Librarian tells Hiro that Rife's archaeological teams have excavated the ancient city where Enki lived and removed many tablets.

Y.T. hooks up with security guru Ng and they go to the Sacrifice Zone to purchase some Snow Crash. Y.T. manages to get a vial of the drug and Ng freezes it before it can self-destruct. Some Rat Things help them, and Y.T. tells Ng that she had once saved a dog who had been shot and named him Fido, but one day Fido was gone. Y.T. wonders if Fido is now a Rat Thing. Y.T. passes the info about the Snow Crash drug on to Hiro. Hiro tells Y.T. that the Snow Crash virus in the Metaverse only affects hackers, and Y.T. tells Hiro that her mother, who works for the Feds, is a hacker. Y.T. goes home, tells her mother about the virus, and smashes her mother's computer.

The next day, Y.T.'s mom goes to work, and is summoned for a polygraph test. The proctors ask her if she believes Y.T.'s story about the virus.

Hiro buys a motorcycle and rides to Oregon. Hiro meets up with Chuck Wrightson, former president of TROKK, who tells Hiro about the Orthos, or Russian Orthodox refugees, who took over his territory with the threat of a nuclear bomb. A bunch of rednecks from a New South Africa franchise try to kill Hiro, but Hiro manages to escape from the rednecks and the Enforcers.

Y.T. picks up a package at Rife Advanced Research Enterprises that is to be delivered to the Feds. When Y.T. drops off the package, the Feds try to kidnap Y.T. who nearly escapes, but a stun grenade knocks her out. Y.T. wakes up in a van, and is transported over a period of days to the Raft, where she is forced to work in a makeshift cafeteria line.

Hiro drives down to Port Sherman, Oregon, the closest land point to the Raft. There are a lot of Russians staying in the hotels, including Gurov, the man who took over TROKK. Hiro manages to get on board the ship Kowloon and meets up with a large group of Mafia boys, including Fisheye. All hell breaks loose around Port Sherman, as all of the Orthos try to escape to a boat in the marina. The Mafia boys thwart their plan by ripping part of the dock carrying Gurov and other bigwigs and towing the dock out to sea. Fisheye tells Hiro that they are all part of Lagos's gang.

Raven arrives on a kayak and cuts the dock section loose from the towboat. A submarine surfaces and rescues all of the Orthos, and Fisheye is mad as hell. The submarine sinks the Kowloon, forcing Hiro, Fisheye, Vic the sniper, and Eliot the Kowloon captain off in a life raft. To pass the time, Hiro hacks the Snow Crash virus from the scroll in the Metaverse and develops a program to counteract it, called Snow Scan. Hiro also develops an invisible avatar, which may come in handy later. When a pirate ship approaches them, the men lure the pirates in and Fisheye takes them out with a blast from Reason, a souped-up Gatling gun. The men take one of the pirates' boats and head towards the Raft.

Y.T. meets Raven, who appears in her cafeteria line one day. Y.T. thinks Raven is sexy in a dangerous sort of way. Raven takes Y.T. out of the line, and brings her to what passes for a restaurant on the Raft. Raven gets a call on the radio, and has to go take care of something, leaving Y.T. in the restaurant.

Hiro and the other men approach the Raft, and are attacked by Raven and a number of other men. Fisheye is killed when Raven throws a spear through him. Eliot and Vic are also killed. Hiro finds that one of the men he killed is a wirehead; he has an antenna grafted into his skull and keeps babbling even though he is dead. Hiro offloads Reason and a few supplies into a dinghy.

Raven returns to Y.T. and they head off to the upscale portion of the Raft where Raven has rented a container to spend his last night here. The two of them start to have sex, but Y.T. forgets to remove her dentata, a device to thwart sexual assaults. The dentata shoots Raven full of sedatives and he passes out. Y.T. leaves the container and connects to the Metaverse at a public terminal.

Hiro finds he can connect to the Metaverse again. Hiro travels to Ng Security headquarters in the Metaverse and meets Ng, Uncle Enzo, and Mr. Lee. All of the men discuss what they know about L. Bob Rife, Snow Crash, and the nam-shub of Enki. Hiro tells them that he is going to the Raft to find the tablet containing the nam-shub of Enki and transmit it to all of the Raft people to break the hold that Rife has on them. The Librarian gives Hiro a virtual map of the aircraft carrier, and Hiro uses Reason to blast a hole in the hull of the aircraft carrier so he can climb in.

Y.T. is recaptured at the public terminal by a wirehead and transferred to Rife on the aircraft carrier. Medics come in to revive Raven. Y.T. is forced on board a helicopter, and sees an ancient tablet on the floor. As the helicopter takes off, Hiro threatens Rife, and Y.T. pushes the tablet out of the helicopter onto the deck of the aircraft carrier.

Rife's helicopter takes off to go to LAX, and Y.T. can see another helicopter flying parallel to theirs. Raven is in the other helicopter connected to the Metaverse.

Hiro is attacked by some wireheads on the deck, but they are subdued by Juanita, who has figured out how to develop nam-shubs of her own. She has been reviewing the tablets on board the aircraft carrier. They pick up the tablet from the deck and Hiro has The Librarian read the text over the communication system of the Raft. Once the nam-shub is released, the control over the people is cut. Hiro connects to the Metaverse and travels to the place where Rife's infrastructure is located. Inside, he sees that the US government had been working on a programming project for Rife. Hiro sees Raven there, picking up a blue shape representing a software bomb. Hiro realizes that this is a Snow Crash bomb, and Raven is planning to nuke the hackers in the Metaverse. Hiro follows Raven out to the Street.

Rife's helicopter lands in L.A. and Y.T. tries to escape, but Rife pulls her back into the helicopter. A Rat Thing in Phoenix named Fido hears other dogs barking about some bad men, and Fido recognizes Y.T. as the girl who loves him. Fido jumps out of his fence and heads to L.A. Y.T. gets the attention of a Kourier who puts out an emergency code to all of the Kouriers. A small army of Kouriers manage to bring the helicopter down. Y.T. escapes from the helicopter and disables it by throwing a harpoon cable into the rotors. Y.T. sees Raven in the other helicopter jacked into the Metaverse. Rife hijacks a pizza delivery car and escapes.

Hiro chases Raven down The Street in the Metaverse. Hiro realizes that his father knew Raven's father, and they discuss this while racing on their motorcycles. Raven enters the amphitheater and drops the Snow Crash bomb on the stage. Hiro cuts him down, and disarms the bomb using his Snow Scan program.

Uncle Enzo waits at LAX for Rife to arrive and carries a new skateboard for Y.T. Sensing something is wrong, Uncle Enzo slips off right before his lieutenant is killed. Uncle Enzo finds Raven. They injure each other, and Uncle Enzo uses the sonic blast from the skateboard to shatter all of Raven's glass knives. The story concludes with the Rat Thing Fido launching himself into L. Bob Rife's private jet, causing it to explode.