RATCATCHER is seen through the eyes of twelve-year-old James Gillespie. Impatient for news of his family's transfer to a housing scheme on the outskirts of Glasgow, James spends the summer playing at a nearby canal, amongst the mounting rubbish (due to a protracted refuse workers strike). Whilst in the water with a neighbour's boy, Ryan, a childish game gets out of control and Ryan drowns. Nobody witnesses the accident and James alone knows that he is implicated in the death. His fascination with the canal escalates and he is drawn to it time and again.

With his growing guilt comes increasing isolation from his family. He feels particularly alienated from his father and when he sees him returning drunkenly home with another woman, he becomes firmly set against him. Nearly everything his father does reminds James what he is destined to become, and he spends less and less time at home, finding his father's oafish, although rarely malicious, presence intolerable.

Drawn to the canal, James meets fourteen-year-old Margaret Anne, a naïve girl whose throwaway observations about the drowning lead James to deny ever knowing the dead boy. He contents himself with the babbling company of the animal-loving Kenny, one of his neighbours, and the bravado of Matt Monroe's gang, who take him to Margaret Anne's flat. There he is expected to keep an eye out for her mother as the gang takes turns in a room with her. The boys egg James on to take his 'turn'. Unexpectedly, a moment of real tenderness passes between them.

One day, seeing his sister get on a bus, he steals a few coppers from his Da and follows her. The urban landscape turns into countryside and at the terminus James wanders around the unfinished houses of a new scheme, discovering a field where he has the freedom to lose himself.

A relaxed intimacy grows between James and Margaret Anne and when alone, they are playful and tender towards each other. At home, Da does not really notice that James is absent a lot these days, seeing a quiet house as an opportunity to nap. One afternoon, he is roused from his slumber by Kenny's mother. Rushing out in his underwear, he saves her son from drowning. Returning home sodden and half-naked, covered in muck and itching from the canal, he is met by council inspectors who have chosen this moment to assess the family for a new house.

Da becomes an accidental hero. The family is in a festive mood when, covered in scabs from the polluted water, Da collects a gold medal for bravery from the Lord Provost. In celebration, the family dance happily together at home while Da goes out drinking. On his way home he is involved in a ruckus with some local boys. Humiliated and drunk he returns in a violent mood and slaps their mother. For James, briefly proud of his father again, this is too much. He runs into the night and heads for Margaret Anne.

A convoy of army trucks arrive in the street to clear the rubbish. James watches the chaos for a while before running into Margaret Anne with Matt Monroe's gang. Feeling confused about his emotions he runs off, until exhausted, he returns home to sleep. The following day, James returns to the canal and dives down into the murky water.

On a bright, sunny day, a procession of people carry the Gillespie family's furniture through James' field as they move to their new life.