Patrick Oxtoby has suffered a mental break, but it sounds like he's been mentally ill for some time. Patrick has just been jilted by his "fiance", his first girlfriend who he had proposed to after only dating 2 months. He stifles an urge to push her down a flight of stairs and decides, instead, that he should just move away.
In the first half of the book literally every conversation is akward. Patrick tries to joke, to flirt or just to partake in the conversation, but as the book is written first person, the narration reveals a methodical reasoning that reminds me of sociopathy.
Patrick's views on women are messed up as well. He fixates on the first two attractive women he meets, and becomes overly protective and posessive over his landlady, and strangely forward, and demanding of a waitress he meets and forges a bond (mostly in his head) with. He describes both women as beautiful, but makes a point of stating that they aren't wearing any makeup.
The day after Patrick arrives, his mother follows him, for some reason upset that her adult son has moved out of her house. She accuses him of leaving in order to hurt her. She fails to pick up any cues as to her unwelcomeness. Patrick stifles an urge to push his mother off a pier, and instead just offends her by bluntly telling her he wants her to leave him alone.
Ian Welkin is one of Patrick's roomates. Welkin comes from a well to do family. He's a charming flirt a drunk and a womanizer. In short Patrick focuses alot of resentment on Welkin, while at the same time rationalizing that he wants Welkin as a friend, more than he doesn't want Welkin as a friend. Theres also sexual tension directed by Welkin on Patrick.
As if you couldn't tell by the foreshadowing, Patrick commits a violent act. He accidentally kills someone. He's sent to prison.
The second half of the book is alot less akwardness. Patrick has a much easier time dealing with his fellow inmates, and even with a creepy guard that wants to help/rape him (he doesn't get raped at this point) Things actually go pretty well until Patrick makes friends with an inmate that wants to be his lover, at which point more powerful inmates threaten to pimp him if he doesn't provide them with money and drugs.
By the end of the book it's evident that Patrick will, once he serves his minimum sentance be in some senses both healed and damaged.