Davey is a 17-year-old boy known for his long hair and for riding his mother's pink bicycle around the island of Inishmore. He accidentally finds himself involved in a dangerous situation when he spots a dead cat on the road and attempts to do the right thing by bringing it to its caretaker. He prefers a quiet, pacifist lifestyle away from paramilitary conflicts, making him an ill fit for the chaotic violence that descends on his town.

Donny is a middle-aged man living on Inishmore who has been tasked with watching his son's beloved pet. He attempts to handle the crisis of the injured animal by getting drunk and formulating an ill-conceived plan with Davey to deceive his violently unstable son. He approaches the looming threat with a mixture of fatalistic panic and dark humor.

Known as "Mad" Padraic, this 21-year-old serves as a second lieutenant in the Irish National Liberation Army (INLA). He operates in Northern Ireland because it provides an outlet for his sadistic tendencies, having previously been rejected by the IRA for being too erratic. Despite his ruthless reputation and willingness to torture, he harbors a deeply sentimental attachment to his pet cat.

Mairead is Davey's 16-year-old sister who desperately dreams of joining the INLA. She protests the meat industry by shooting out the eyes of cows and aggressively flouts traditional femininity by cutting her hair short and wearing military-style clothing. She is an exceptionally skilled marksman with her air rifle and demands respect from the older men around her.

Christy is a Northern Irish member of the INLA who wears an eyepatch due to a past incident involving Padraic. He travels to Inishmore with a convoluted scheme to lure Padraic home, using aggressive nationalist rhetoric to justify his sadistic and often illogical orders. He demands absolute loyalty from his subordinates.

Joey is a junior member of the INLA who travels to Inishmore alongside Christy and Brendan. He is the only member of the trio who openly displays a conscience, particularly regarding the group's cruelty toward animals, which brings him into direct tension with his violent superiors.

Brendan is an INLA member operating under Christy's orders. He readily goes along with Christy's violent schemes to eliminate Padraic, lacking Joey's moral reservations and fully participating in the group's chaotic infighting and cruel tactics.

James is a low-level drug dealer who sells marijuana to college students. He demonstrates acute self-awareness while enduring physical torture, using quick thinking to assess his captor's weaknesses in hopes of surviving his brutal punishment.

Wee Thomas is Padraic's black cat, described as his only friend for the past fifteen years. He acts as the emotional center of Padraic's life and the primary catalyst for the escalating conflict on the island.

Sir Roger is Mairead's orange cat, named after the Irish nationalist Sir Roger Casement. He possesses a distinct, somewhat snooty personality and becomes an unwilling participant in Davey and Donny's desperate cover-up attempt.