Merle Jones was introduced when Joan Ferguson arranges her transfer from C block as muscle to support Kath Maxwell, who Joan is trying to set up as top dog on Wentworth. It is stated that Merle should not really be in prison at all, but in some other secure institution. Her low mental age gives rise to her nickname "Loony", but she is not mentally ill, though her confusion often expresses itself violently. Although she may be Kath's protector physically, emotionally she becomes a substitute daughter for her, and this aspect of their relationship is well handled and manages to be touching without being over-sentimental. She bumps Lorelei Wilkinson over while running to the gym and didn't even notice, attacks Rita Connors in the Gym, Alice Jenkins and Lexie Patterson have trouble stopping Merle and she pushes Lexie into one of the machines. Merle feels guilty of what happened. She takes things that don't belong to her. She took a toy that had cocaine in it and thought it was plutonium. She takes stuff off the art wall in the rec room. She knocks out Rita when she makes fun of her. She would attack anyone for not paying protection money to Kath when Kath takes over as top dog. Merle is very protective of Kath. When she is utterly betrayed by Kath when she abandons her during an escape attempt, Merle has a breakdown and is transferred to Ingleside mental hospital. Marty Jackson is mainly responsible for her recovery and return to Wentworth, where she is reconciled with Kath in the penultimate episode.

Merle is known for attacking (or in her words "bamming") anyone who calls her "looney", she even attacked a prisoner and they spent six months in hospital for it.

Merle uses the words "bam" and "biff" when she talks about attacking people. "I'll bam you!"