First Appearance: Episode 387 (1984)

Last Appearance: Episode 584 (1985)

Known Family: Mother - Heather O'Brien; Father - Mike O'Brien; Brother - Jeff O'Brien (d. 1985); Uncle - Jim O'Brien

Key Relationships:
Flings with Terry Hansen, Wayne Hamilton, Alan Brandon and Gary Evans

Key Storylines:
Katie moves to Albert Park, Melbourne, with her parents, Mike and Heather, and younger brother, Jeff, in 1984. Her first priority is to find herself a job - and she persuades her father to take her on in his lawnmowing business, so that she can use the money she earns to buy herself a computer: her dream is to develop a career writing computer games. She finds herself attracted to both Andy Green and John Palmer, but nothing happens with either of them.

When businessman Roger Carlyle turns up in Albert Park, Katie is worried: Heather used to work for Roger in Perth but has always warned Katie to have nothing to do with him because of his interest in young girls. However, when Roger offers to help her with some contacts who might be interested in her computer games, Katie finds herself unable to say 'no'. Unfortunately, when Katie signs a contract for her games, she discovers later that she's signed away exclusive rights to every game she ever comes up with. She blames Roger for misleading her - but, to her surprise, Roger agrees to help her again by threatening to take away all the business he puts his contact's way. Roger's son, Luke, warns Katie that Roger is only being so nice to her because he's a letch and he wants her. Katie challenges Roger about this - and is astonished when he admits that Luke is right. He then assures Katie, though, that he's decided not to do anything about his feelings for her.

Katie finds herself attracted to Terry Hansen - but after discovering that he raped Jill O'Donnel, she runs a mile. She calms down, though, and when Terry goes on trial for kidnapping his baby daughter, Fee, Katie stands by him. Terry is sent to prison in Ararat. Katie visits him whenever she's able, but she's left devastated when Terry sends her a letter in which he tells her that he's grateful for the way she's stuck by him, but that the last thing she needs is to be tied down with a guy with his sort of responsibilities.

Katie meets Wayne Morrell when he's in Melbourne on business. He takes an interest in her computer games and offers to help her with some contacts if she's ever in Sydney. After the way things have been in Melbourne, it doesn't take Katie long to decide to move to NSW, where she moves into Fiona Thompson and Irene Fisher's boarding house. Wayne helps Katie land a contract to develop new computer games - and as the two celebrate together, a passionate kiss ensues. Katie quickly falls in love with Wayne - despite being warned by several people that he's bad news. She's therefore devastated when, just a short time later, Wayne tells her that he thinks it's best if they end things, as there's no chance of their relationship lasting forever. He later reveals, however, that Karen Fox blackmailed him into ending his relationship with Katie, but has backed down, meaning they can be together again.

Wayne comforts Katie after she learns of the death of her brother, Jeff, in a fire at the O'Brien house in Melbourne. He then turns to Katie for support after rejection by his father, Gordon, and business problems caused by Karen Fox. However, when he tries to take things further than Katie - who's a virgin - wants, Katie pushes him away. Wayne reacts badly, accusing her of thinking only of herself. The relationship comes to an abrupt end and Katie moves back to Melbourne.

Katie soon finds Karen's son, Alan Brandon, taking an interest in her - but when he, too, tries to take things too far, Katie rejects him as well. After another altercation with Wayne, in which he ends up snarling that Katie is a stupid, frigid bitch, a horrified Katie tries to prove him wrong by dressing-up provocatively and coming-on to Andy Green. Andy, however, sees through her act and accuses her of being a mess. An upset Katie concludes that nobody wants her. However, when Alan asks for a second chance, Katie agrees - and when Alan tries to take things further this time, she lets him. Things don't get very far, though, because they're sprung by a furious Beryl Palmer, whose bedroom they're using!

Alan is badly injured when he's caught up in the explosion of a boobytrapped wheelchair during a party at David Palmer's house in the country. When Katie goes to visit him in hospital, she meets surgeon Dr. Ross Newman - who quickly charms her and invites her out for a drink. It's Ross to whom Katie loses her virginity, after he gets her drunk. The relationship develops - but sadly, Katie discovers that Ross is two-timing her with Barbara Hamilton. A distressed Katie realises that she's once again fallen for the wrong man.

When she then discovers that Ross may have kidnapped Beryl Palmer's baby son, Robert, Katie decides to try and find out if Ross is really behind it by pretending to Ross that she forgives him. The plan almost works until Ross discovers Katie going through the pockets of his jacket. He flees, leaving Katie annoyed that her plan didn't work.

Katie moves back to Sydney, where she moves into Charlie Bartlett's house. When Wayne asks her to use her computer to hack into the Hamilton company's accounts, his reasoning - that he thinks the accountant is ripping-off the company - is plausible enough for Katie to agree, albeit reluctantly. She writes a program that provides Wayne with access to all the company finances - but she then becomes suspicious about his actions and reports them to Stephen Morrell. There's a shock in store for everyone when it turns out that the Wayne who was trying to rip Gordon off wasn't really Wayne: it was a lookalike named Gary Evans!

Mike and Heather announce that they've decided to start life afresh in Queensland and Katie decides to go with them, leaving all her problems in Melbourne and Sydney behind.