In the Belly of the Beast is long-time inmate Jack Henry Abbott's personal account of his time in prison. He explains what goes on in prison and the devastating psychological effects he and others like him have suffered.

Abbott has been jailed from a very young age, having spent time in juvenile and then adult facilities since he was twelve. He was a foster child and initially jailed for "failure to adjust to foster homes." Later he was jailed for passing bad checks; his only serious crime while out of jail was armed robbery when he briefly escaped from prison in the early 1970s. He has spent more than twenty years in prison because of his belligerence and continued acts of defiance while in prison.

To Abbott, the American prison system is unjust, cruel, and oppressive. He cannot adjust to prison, and so he lashes out and ironically perpetuates his time in prison. He does not believe his prison sentence is his fault; on the contrary, he would like an apology from the prison system.

The prison system treats men like children and so creates "arrested adolescences" or emotionally stunted men. Abbott has been subjected to the worst prison has to offer, including blackout cells (sensory deprivation cells where no light shines), and "the hole," solitary confinement where he has been subjected to starvation diets and forced administering of psychiatric drugs, to the point of near-insanity and death.

"Pigs," as Abbott refers to the guards are universally violent and tyrannical. They are allowed to do any violence they like to prisoners, as there are no consequences. Abbott claims he has been accused of many acts of violence he was not guilty of by vindictive guards, which then leads to further punishment and prison time. Guards are evil because the state gives them absolute control over prisoners, and they become corrupted with this power.

Prisoners live by a code of violence and murder. The only thing that is respected is moral strength and the threat of violence. A long-term prisoner must be capable of murdering someone in order to survive. Abbott also describes the frequency of homosexual acts in prison, in which "punks" service their masters. These acts are not about sex or affection, but a display of power, and rare is the prisoner who actually thinks of such acts as homosexual.

Abbott has found comfort in the form of drugs, including heroin and marijuana, and philosophical reading. He is especially enamored of Marx and of Communism. He believes Communists are the only ones capable of honesty in describing the tyranny of America and its prison system. He considers himself somewhat of a revolutionary and is looking forward to the day that Communists spark a worldwide revolution, which would end (in Abbott's mind) the oppressive police state. Like Marx, Abbott believes history is a class struggle.

Abbott equates classism with racism. History has been an effort by whites to assert superiority over non-whites. Racism is rampant in prison, with guards stirring racial animosity and non-whites asserting the dominance that society has otherwise robbed from them.