Part one
Mouse introduces herself, and mentions her involvement in Paulie's "weird, Napoleonic act of self-assertion", though she does not specify exactly what it was that Paulie did, or even who she is. Mouse speaks of her distracted father, Morley, and her critical stepmother, Sal. She also tells the reader of the hump she has in her left shoulder as a result of a childhood bout of polio, which developed into kyphosis. Mouse has named the hump Alice, after her dead mother, and says that the hump is like a friend to her. Throughout the novel, Mouse's conversations with Alice provide comic relief and exposition on the story's dark events. In the second chapter, Mouse pauses the narrative and recounts details from Paulie's trial, something she continues to do sporadically throughout the novel. It emerges that Paulie committed a murder of some kind.
Mouse recalls how she was sent to the boarding school in Toronto- Bath Ladies' College- because her father had "an unfortunate inferiority complex about bringing up females" and because its headmistress, Vera Vaughan, was a distant cousin of Morley's. Mouse is nervous, keenly aware of her shyness and her physical shortcomings, and is bewildered by the strange atmosphere of the old-fashioned school. She meets the friendly janitor, Sergeant (who is a dwarf), and Paulie's brother, Lewis, whom she later catches shaving in her new dorm bathroom. Mouse meets Tory and Paulie that evening, immediately warming to the friendly Tory and taken aback by Paulie's brash manner. It is clear that, different as they are, the two have a very close friendship. Tory tells Mouse that Paulie's brother, Lewis, is her boyfriend, and that they are in love.
Mouse settles quickly, but not comfortably, into the school, picking up the lexicon and the consensus regarding the staff of the school amongst the students. The intensity of her fixation with John F. Kennedy is evident in the long, familiar letters that she sends him on a regular basis.
To both Mouse and Paulie's chagrin, Tory breaks her leg in a field hockey accident and is sent home for the rest of the winter term. Tiring of Paulie's volatile behaviour, Miss Vaughan orders Paulie to 'walk off' her frustrations at the school every evening after class, and assigns Mouse to accompany her. The two form a kind of bond, and Paulie soon reveals to Mouse that she doesn't have a brother named Lewis; it is actually her, masquerading as a boy, and that she has everyone fooled, even Tory. She takes Mouse to the shrine she has made to the 1933 film King Kong , and sets Mouse a series of bizarre tests to prove that she, too, can 'be' a boy. These include: eating six bowls of tapioca pudding without vomiting, letting a match burn to the skin without crying, and managing to urinate whilst standing up.
After Mouse completes these 'preliminaries', she embarks upon three major tests: mastery over other men, mastery over women and mastery over nature; in the first, Mouse creates her male alter-ego 'Nick the Greek', and dresses as a boy for the first time. Mouse and Paulie pick a fight with boys from the nearby King's College, one of whom is Tory's elder brother, Rick. In the second, Paulie challenges Mouse to seduce an overweight girl from the local convent school, which she does, though the outcome borders on comical; the girl in question, Josie, is found to have known all along that 'Nick' was a girl, and bursts into tears when Mouse hesitates to caress her. In the third test, Paulie challenges Mouse to kill a pigeon.
Mouse's reluctance to do these tasks emphasises that her wish to be a man is not founded on a genuine desire to become one, or even on an attraction to girls. Rather, Mouse longs for the freedom that the men of the time enjoyed, which she believes she will never be able to experience as a woman.
In Tory's absence, teacher's pet Ismay Thom moves into Mouse and Paulie's dorm room. Her pushy presence aggravates Paulie, but Mouse warms to Ismay's eccentric but likeable character.
Paulie leads Mouse in a break-in to Mrs Peddie's private quarters, where they stumble upon correspondence between Miss Vaughan and Mrs Peddie, written years before. The letters detail an incident in which Miss Vaughan was assaulted by a police officer, who had seen her kissing Mrs Peddie. Paulie steals them, and hides them in Mouse's bedside drawer. When Mouse checks on them in the morning, they have disappeared.
In Tory's absence, Paulie's behaviour worsens, and she is banned from attending the Visitor's Luncheon at King's College. Mouse is taken there by her Uncle Winnie (her mother's brother) and his wife. Whilst there, she sees Tory with Lewis in the yard outside. Lewis is chased from the school, after being seen vandalising a statue. Amidst the uproar, the news is broken that President Kennedy has been assassinated.
Mouse is devastated by the news of the President's death, but is cheered by letters from Jack O'Malley, a King's College student she met at the Luncheon. Paulie's behaviour becomes increasingly sinister; she instructs Mouse to beat her with an old cane, and when she hesitates, Paulie beats her with it instead, hard enough to draw blood. Mouse admits that she continued to go along with Paulie's tests because Paulie's evil character absolves her of all the things in her life that she cannot change (i.e., not being worthy of Morley's love, not having any friends) and makes her even more innocent.
After performing in the Christmas show, Mouse is summoned to Miss Vaughan's office, where she is told that Morley has died from a sudden heart attack.
Part three
On returning to school, Mouse discovers that Paulie has been removed from her dorm room, replaced by Asa Abrams, and that Tory has returned. To her surprise, she receives quiet sympathy from her peers as well as her teachers, and is particularly touched by Tory's gift of a New Testament bible. Paulie has been forced to take Asa's old cubicle. Her exile makes her noticeably friendlier to Mouse. Paulie discloses that she (as Lewis) got into a fight with Rick and injured him with a knife, and that Tory was upset with her for doing it. Ismay tells Mouse that Paulie has been carving lurid stick figures on her bedstead and stealing her music scores, which Paulie laughingly denies.
Lewis drives Mouse to King's College on the evening of the Christmas dance, to pick up Jack O'Malley. The two make awkward conversation as Lewis drives to Canon Quinn's house to pick Tory up. Mouse sees Rick and Lewis arguing and scuffling at the door of the Quinns' house; Lewis returns to the van noticeably upset and without Tory. Once alone, Lewis reveals to Mouse that Rick had challenged Lewis to prove he was a boy by showing him his penis, and begins to cry.
Mouse eventually leaves Paulie, and joins Jack inside. They become involved in the festivities, drinking gin and "fooling around for the longest time standing up". Toward the end of the evening, Mouse breaks away and searches for Paulie, finally finding her in the tower washroom, her hair shorn and her face cut and bleeding. Paulie angrily brushes Mouse away when she tries to comfort her, and says that she's not giving up on Tory. They are distracted by Sergeant, who has dressed up as the school's dead founder, Miss Higgs, for the evening, and is tearing round the school on an antiquated Victorian bicycle. The girls try to follow him, but Mouse loses Paulie in the darkness. She looks for her in her room, and discovers Ismay's musical scores in there, along with pages ripped from her father's Gray's Anatomy ; the pages depict the male penis, and have been annotated by Paulie. Tired, and tipsy from the alcohol Jack gave her, Mouse goes to bed.
Mouse wakes early the next morning and, worried by Paulie's prolonged absence, goes to look for her in the tunnels beneath the school. She finds Paulie distressed, saying that Sergeant has fallen against one of the heating pipes and hurt himself. She takes Mouse to his prone body, then sends her to get the Czech groundskeeper, Willy. Sergeant is unconscious, and badly burned from falling against the scalding pipes. When Mouse returns with him, she finds Sergeant dead, and Paulie gone. Remembering what she found the evening before, a horrified Mouse suspects what Paulie has done. Lifting his costume skirts, Mouse sees that Sergeant has been castrated.
Mouse recalls details from Paulie's trial, and informs the reader what happened next; after removing Sergeant's genitals with one of Morley's scalpels, Paulie had stuck them to herself with tire glue, and presented herself to Rick Quinn in her chilling garb. She was arrested shortly after, and found to be too mentally unstable to take full responsibility for her actions; eluding jail, Paulie was sent to a mental institution for "rehabilitation". Tory was sent to another school (though the court heard that she continued to see Paulie whilst she was in custody), and Mouse was sent home to Madoc's Landing until the furor over her involvement in Paulie's crime had died down. She recalls a dream she had about Sergeant after his memorial service, and says she's glad that he didn't know it was not his friend Lewis who had killed him, but Paulie.
Now sixteen, Mouse looks back on her time at Bath's College, crediting the girls and women there who inspired her to be herself, and signs herself off as 'M.B.'
