Every Day Is Mother's Day by Hilary Mantel
Evelyn Axon is a medium by trade; her daughter, Muriel, is a half-wit by nature. Barricaded in their crumbling house, surrounded by the festering rubbish of years, they defy the curiosity of their neighbors and their social worker, Isabel Field. Isabel is young and inexperienced and has troubles of her own: an elderly father who wanders the streets, and a lover, Colin, who wants her to run away with him. But Colin has three horrible children and a shrill wife who is pregnant again - how is he going to run anywhere? As Isabel wrestles with her own problems, a horrible secret grows in the darkness of the Axon household. When at last it comes to light, the result is by turns hilarious and terrifying.