Carmel Finnan was a student nurse classmate of Martin Platt's who babysat Nicky, Sarah Louise and David in September 1992. As she proved to be good with the kids, Gail and Martin started calling on her regularly and soon trusted her enough that they left her to watch them when they went away for a couple of days.
Carmel lived alone at the nurses' home after moving to England from Ireland. She was born out of wedlock to a fifteen-year-old mother and brought up by her grandparents as their own child. When she found out the truth about her parentage at fourteen, she disowned her family and took up with the McGuires, who owned the neighbouring farm to her own family's. There, she became obsessed with Michael McGuire and accused him of fathering her (non-existent) child. Her grandparents placed her in hospital which she left after a year apparently a fine, cheerful woman who had put her dark past behind her.
Now leading a lonely life in another country, Carmel started to get her feet under the table at the Platts'. When she was frightened by a prowler at her digs one night, Carmel was invited by Gail to stay at 8 Coronation Street. Gail and Martin then invited Carmel to lodge with them until she found other accommodation, sharing Sarah Louise's room, and she happily accepted.
Over the following weeks, Gail and Martin realised there was another side to Carmel. Martin became Carmel's new obsession and she convinced herself that he was secretly in love with her. Firstly, she "forgot" to tell Martin that Gail was coming home late, leading to an argument between them although neither of them realised Carmel had orchestrated it. Carmel told Sally Webster that Gail and Martin were having marriage problems, which Sally knew wasn't true, but when Sally confronted her about telling lies, Carmel started crying and accused Sally of wanting to cause trouble and told Gail that Sally didn't like her. Gail didn't know what to believe but was growing tired of Carmel constantly being around and monopolising the kids. Further concern was raised when Percy Sugden, as Bettabuy's Father Christmas, overheard Carmel telling a woman that David was her son. Carmel explained it away that she had pretended so that a woman wouldn't get at her for being a baby-sitter.
When Alf Roberts was in hospital with food poisoning, Gail and Audrey stayed overnight there. Carmel was laying in Gail and Martin's bed when a drunken Martin got home late, unaware that Gail was away, and it wasn't until morning that he realised he was in bed with Carmel. He demanded an explanation but Carmel frustrated him by acting like it was normal, and then thanking him for a wonderful night and confessing her love for him. Martin couldn't remember what had happened but was sure he'd never be unfaithful to Gail and made Carmel leave for Christmas in Ireland early.
Carmel returned suddenly on Christmas Day, telling everyone she had missed the boat to Ireland but admitting to Martin that she had returned as she missed him. She resumed her campaign to get Martin to tell Gail it was over, but Martin told her she was living in a fantasy land and threatened to tell her parents and her tutor if she didn't move out of No.8. Don Brennan helped Martin out by putting him onto a bedsitter, but when Martin took Carmel to a bedsit, she made a move on him and asked him to live there with her, refusing to believe that her feelings weren't mutual. Martin had to fight her off and, back in Coronation Street, he threw her bags at her, telling her to leave. Carmel told Gail that she and Martin loved each other but Gail thought she was trying to cause trouble and threw her out.
In the New Year, Carmel ignored Martin at college, much to his delight. Carmel however was deeply upset and in March she turned up at No.8 and told Gail and Martin (and Ivy Brennan) that she was carrying Martin's baby. Gail didn't believe it at first but Ivy found out from Don that Martin had woken up in bed with Carmel and told Gail, who began to doubt Martin's honesty. After convincing Gail he'd been faithful, Martin decided to give up his course as it seemed the only way to cut Carmel out of their lives. When Carmel found out, she accused Gail of making Martin leave college and told her she'd take Martin from her. Carmel tried to snatch David while Sally Webster was minding him but left when Sally threatened to phone the police. On learning about the incident, Gail confronted Carmel at her bedsit, only for Carmel to deny the incident had occurred. They had a scuffle on the stairs which ended with Carmel falling down and breaking her leg. Gail was worried that she'd hurt Carmel's baby but when examined it was revealed that Carmel wasn't and never had been pregnant.
Carmel conceded that she wasn't pregnant but pressed charges against Gail, telling the police that Gail had pushed her down the stairs in a jealous fit. Martin had to be escorted out of her ward when Carmel told him and Gail that she knew one day she and Martin would have a baby, still unable to accept the truth. A short time later, her grandfather John Finnan arrived in Weatherfield to question the Platts. When he realised the similarities to Carmel's obsession with Michael McGuire, he apologised to the Platts and told them that he would get Carmel to drop the charges and take her home to Ireland to get the care she needed.