33 Snowfish follows the character of Custis, a 10-year-old orphan living with his "owner" Bob Motley, who sexually abuses him, in a dilapidated house in Rockdale, Illinois. After overhearing that he was to star in a snuff movie, Custis steals a small pistol and escapes through a hole in the wall. While hiding from Motley's crew and begging for quarters in a video arcade at the Joliet Mall, Custis spots Boobie (whose real name is Darrin Flowers), a strange boy with black eyes and a single painted fingernail. Custis decides to follow Boobie into Crazy Lou's Woods, a private woodland supposedly owned by an ex-military cat farmer. Custis and Boobie soon become friends.
Custis, having no home, and Boobie, who has an unstable relationship with his parents, set up a makeshift home in the woods with a tent and steal electricity from a nearby paper factory. Soon they are joined by Curl, Boobie's 14-year-old girlfriend who is addicted to drugs and supports herself as a prostitute, and finally Boobie's baby brother, whom Boobie abducts after murdering his parents. The four of them take to the road in a stolen Buick Skylark to flee the police who are searching for Boobie, engaging in dumpster diving, robbery and begging in various Chicago suburbs along the way.
Custis – A 10-year-old homeless boy who escaped from a child pornography operation. Custis carries a loaded handgun (a "gat") with three bullets and a broken trigger. He suffers from a seizure-like condition that he refers to as "migration (sic) headaches" which cause him to black out and wake up in different locations. He has frequent dreams about a mysterious individual called Big Tiny, who was said to have been his mother.
Curl – A 14-year-old girl from Bolingbrook, Illinois, who used to live with her disabled aunt Frisco who forced her to turn tricks in their apartment. Curl is kind-hearted, acting as an older sister to Custis, as well as extremely superstitious, believing that she had met Boobie because she sat on top of a pile of Chex cereal on the first of May. She expresses a desire to settle down and marry both Custis and Boobie.
Boobie (Darrin Flowers) – A 17-year-old boy from Joliet, Illinois who is a violent pyromaniac. Boobie rarely speaks, choosing to express himself via his drawings. He is possessive of Curl and extremely protective of Custis, with whom he shares a special friendship. Boobie eventually murders his parents and abducts his infant brother, and goes on the run from the police in a stolen Buick Skylark.
Boobie's brother – An unnamed infant who sleeps in a gutted Magnavox TV in the back of Boobie's car. He has blue eyes and an odd seam down his forehead, for which he is thought to be unintelligent or defective by the others. He is regarded as a likely source of income if he can be sold.
Critical reception for 33 Snowfish has been positive, with the School Library Journal writing "Rapp’s spare text and multiple points of view (Boobie speaking only through drawings) elevate what could have been a preachy sob story to a literary achievement".Kirkus Reviews praised the book's depiction and voices of the main characters.Publishers Weekly stated "Readers may have trouble stomaching the language..., as well as the horrors so flatly depicted and, in the end, so handily overcome."