|“||It's as only as real as you let it be.||”|
Zimmy is a thin girl with grey tinted skin, long black hair and pointed teeth. Her most striking feature is the black material that usually covers her eyes, which Tom has said is a sort of "visual metaphor[sic]". The black mess covering her eyes dissipates whenever Zimmy stands in the rain, revealing two scarlet red eyes underneath. The rain must be natural; artificial rain has no effect. Zimmy doesn't seem to care about her physical appearance. Her hair is tangled and messy, her school uniform is usually in disarray, and she doesn't take showers as much as she should. She is usually seen frowning or grinning mischievously.
She has a generally grumpy attitude, displaying a short temper and a general disdain for those around her, with the notable exception of Gamma, and, later on, Antimony Carver as well. In general, she tends to avoid other people, and doesn't like to be watched. The horrific hallucinations she experiences daily due to her abilities have left her paranoid and prone to mood swings. She has also been shown to have a mischievous, if somewhat dark, sense of humour. She speaks with a broken Birmingham accent and has a tendency to swear more than the other characters.
Zimmy has displayed the ability, both willingly and unwillingly, to project the conscious and subconscious thoughts of herself and others into a form that can be seen and interacted with by others. She experiences these abilities as frequent horrific hallucinations. Consequently, she views her abilities as a curse. As part of her hallucinations, she sometimes ends up in a Birmingham-like city populated by faceless people. Unfortunately, she cannot tell these people apart from real ones, as even the real ones look faceless to her.
The only person who can quell these hallucinations is Gamma, as they disappear when she's near Zimmy (although Annie has a similar effect, if somewhat less effective) and for her to utilize her abilities, Gamma must not be present. However, the often macabre freakish nature of these powerful projections mean that they are capable of being incredibly dangerous when Gamma is not alleviating them, hence her constant companionship with Zimmy. Zimmy never sleeps, which makes it difficult for Gamma, who can only suppress Zimmy's hallucinations while awake.
During storms, Zimmy runs outside and lets the rain wash over her. Her body sizzles and actually releases rivulets of steam, and the covering on her eyes is completely washed away, revealing her red eyes. 
However, rain released back into the skies from the Power Station doesn't work, since it is after the station has taken away the water's natural source of etheric energy.  Standing in the rain is the only time when Zimmy is at least a little happy, as it temporarily alleviates the hallucinations that constantly plague her. During this short period, Zimmy displays a degree of playfulness and rationality that is not often seen from her.
Zimmy's abilities also extend to detecting to etheric connections, communicating telepathically (only seen with Gamma), entering a room undetected, hearing thoughts (seen briefly with Kat) and manipulating memories., , ,
Zimmy was born with her powers. She once had parents, but apparently left them to live on the streets. Tom has stated that they don't remember who she is and if they could, they would be glad that she left.
Nearly a year and a half (one year and 102 days) before Chapter 11: Dobranoc, Gamma, she was alone and wandering the streets of Birmingham. That day, she met Gamma Czarnecki for the first time. 76 days later, they see a creature that looks somewhat like a Rogat Orjak. She and Gamma live together for some time, sometimes sneaking into and occasionally meeting up in a toy store whenever they were separated.
After months of seemingly living on the streets, two employees of The Court come and offer them complete freedom to go wherever they please in exchange for living at the Court, which they accept.
On The Court
When Zimmy is first seen in the Court, she and Gamma are participating in the science fair. Her experiment has not been revealed, but Annie and Kat initially suspect her of tampering with the other projects, since hers was the only one not destroyed. In reality, the culprit was Reynardine, and Annie apologized, but the incident started their relationship on somewhat of a bad note.
Later, Zimmy and Gamma come to Annie for help. Gamma can only chase away Zimmy's hallucinations while she's awake, but she's very tired, and they need Annie to stay with Zimmy while Gamma rests. Apparently Annie's abilities have a similar, albeit weaker, effect on Zimmy as Gamma's. Just before a storm breaks out, the three goes outside. When it starts raining, the drops boil on Zimmy's head, resulting in her becoming very playful and a much better mood as the black gunk around her eyes disappears, displaying the true color of her eyes.
The duo later comes up to the roofs of a building around The Power Station because it messes with Zimmy's head. There are other kids there, which they at first think are projections of Zimmy's mind. As they stand on the rooftop, the station starts some sort of procedure where it drains the water in order to form clouds and then sends off an electrical charge into the horizon. Zimmy gets very disappointed when she realizes the rain doesn't have the same effect as it had before, and as her frustration builds up, she ends up in Zimmyngham with Gamma, Annie, Kat, and Jack Hyland. Eventually Zimmy, Gamma, Kat, and Annie get out without damage, although one of Zimmy's Whitelegs attach itself to Jack.
In her next appearance, she seems to have some sort of hallucination, thinking that she's Annie walking around in Zimmyngham. When she sees how close Gamma gets to Annie, whom she thinks is herself, she snaps and remembers that she is, in fact, Zimmy. It then starts raining, and they are all taken out of Zimmyngham. Zimmy then grabs the Whiteleg on Jack's head and squashes it.
After Annie collapses as a result of Anthony's experiment, Gamma tries to get Zimmy to go help her, an idea Zimmy vehemently resists. Gamma eventually convinces her, however, and they go to Annie's hospital room. Both are able to see a pigeon on top of Kat's head, displaying her true thoughts about the situation. Zimmy comments on Kat's headband, asking her if she's trying to "remind people yer still a girl", to which Kat responds very defensively. Through looking into Annie's dreams, she is able to reach Anthony and psychically punch him. Zimmy then knocks out Shadow, Robot, and Renard, and Gamma leaves, allowing Zimmy's abilities to run wild without inhibition. By looking into Annie's dreams, she is able to connect with Anthony's experiment and punches him, knocking her out of the dream and back into the hospital room, although she continues to hallucinate. In her hallucination, Zimmy calls Annie's father a jerk, causing Annie to throw her across the room within the hallucination, although in real life, Zimmy actually falls while Annie remains motionless. Zimmy comments that Annie has her fight back, and is shown to be afraid of Kat while still in her hallucination; Gamma then returns, and when Kat asks Zimmy why she came if she was so scared, Zimmy tells her that "you can't always run from what scares ya". Gamma takes Kat's headband, and the two disappear.
She and Gamma share an unexplained telepathic connection, and they communicate to each other solely through this way. As a result, she and Gamma have developed an extremely close relationship, to the point where Annie has referred to the pair as an "item", something Tom has confirmed. Zimmy herself has said that she loves Gamma and wouldn't be alive it it weren't for her. Zimmy's love for Gamma has shown to be somewhat possessive, as seen when she translated what the students said to Gamma as insults and flew into a rage when the Antimony (as Zimmy) got too close to Gamma in Zimmyngham.  
Zimmy is cautiously indifferent about her. She sees that Antimony doesn't give her too much trouble and even helped her and Gamma a couple times, so she tolerates her.  She usually calls her "Carver" rather than Antimony or Annie.
Zimmy knows Jones, and Jones knows Zimmy well enough to know the extent of her powers as well as her personality.
See Word of Tom: Zimmy and Gamma for more.
- Zimmy's true name, Zeta, is taken from the eponymous sixth letter of the Greek alphabet. It is also the spoken form of the Latin letter Z in British English. The lowercase form of Zeta is ζ.
- Zimmy and Gamma are one of the oldest characters in the story. Tom came up with them years before writing Gunnerkrigg Court, and they were originally supposed to be characters in a scrapped comic called Alphabet Soup.
- Zimmy's theme song is "Stress" by Justice.
- Tom has stated Zimmy's abilities are at least partly inspired by the effects of panic attacks.