Dougie, a truck driver, is killed while protesting against his company that made him redundant by introducing
self-driving trucks. His wife, Maureen, and their teenage son, Boyd move from
Watford in eastern England to the small town of Sile in the
Pennines in northern England. There Boyd finds his mother's behaviour becoming more and more erratic, and a strange
mould starts appearing on the ceilings and walls of their house. Despite Boyd's best efforts to look after her and keep their house clean, Maureen disappears one day. By now the mould is out of control, and Boyd abandons the house. Boyd meets Leigh, a young woman who works for Gaff, a
scrap merchant. She lets Boyd share her trailer with her, and together they scavenge a local
dump site looking for anything of value for Gaff. One day, on a mound of rubbish, Boyd finds a baby girl. He names her Lamb, and Boyd and Leigh take her in. They assume the arduous task of bringing her up, but Lamb turns out not to be a normal child. She develops far too quickly, and soon the same mysterious mould starts to appear in Leigh's trailer. In a
backstory, Maureen's childhood with her mother, Joan is revealed. Like Lamb, Maureen also undergoes an accelerated development. As a child, and far too advanced for her age, Maureen has several miscarriages. Joan refers to them as "bad copies", and they bury them in their vegetable patch. Later, and despite Joan's warning that Maureen must not leave their house, an inquisitive Maureen sneaks out one night, and meets a young truck driver named Dougie. Back in the present, Boyd, looking for clues as to his mother's whereabouts, returns to their house in Sile. It has been completely colonised by the mould, but under piles of rot and decay, he finds a photograph with an address on the back. Boyd returns to the
landfill and, using Gaff's beat-up van, he takes Leigh and Lamb across the country to the address in the
Cotswolds to find his mother and the truth about Maureen and Lamb's origins. ==Critical reception==