In the deepest, grimiest, saddest part of Coketown live the factory workers – the slang term for them is "Hands." (It's their bosses' slang, and it's pretty demeaning.)
One of these workers is Stephen Blackpool, whose life has been difficult, and who is "a man of perfect integrity." After his day is done, he stands in the street waiting for Rachael, another factory worker, whom he is clearly deeply in love with. They walk home together, talking quietly. He thanks her for always making him feel better by her kind presence. He drops her off at her house, then walks into his own.
Stephen is shocked and dismayed to find there… his own wife! Who is now a really, really super-mega-awful alcoholic disaster. This explains both why he's always in such a bad mood, and why he and Rachael can't get married.
She is mildly lucid, and he asks her why she has come back despite the fact that he pays her to stay away. She cackles like a monster and says that she will never really leave him alone, then passes out on the bed.