The book focuses on Violet Adams, an already-skilled inventor who wants to attend the prestigious and selective Illyria College. The problem is that they don't accept women, so she hatches a plan with her brother Ashton to disguise herself as a man and attend under his name. As the year progresses, of course, things get more and more complicated, and it gets harder to keep up the pretence. She and Duke Earnest (the hereditary headmaster) end up falling for each other, only Earnest doesn't know that "Ashton" and his eccentric sister Violet are the same person, and he's consequently quite confused about everything. Plus, the Duke's young ward, Cecily, also thinks she's in love with "Ashton". Meanwhile, Violet is getting caught up in the problems of her new friends, involving various romances and some unpleasant blackmail. Finally, there seem to be killer robots marauding around the basement, a legacy of the current Duke's father and his schemes for world conquest. These plots all come together at the end.
The book contain examples of:
- Blackmail: A fair amount of it.
- The longest and most sinister is by the student Volio towards Cecily's governess, Miriam. When Volio gets wind of the fact that Miriam isn't as prim and proper as she appears, and is in a relationship with a student, he tries to force her to act as a go-between and advocate between himself and Cecily, with whom he thinks himself in love. (He raises the possibility of demanding sex from Miriam too, but she tells him she would tell Cecily and thereby guarantee his rejection.) Miriam pretends to agree to help him woo Cecily, but in fact, she and her friends generate correspondence from her instead.
- Volio also sees the Duke and Violet-as-Ashton kissing, and tries to use this against the Duke. This one doesn't work either.
- The actress/prostitute Fiona, hired briefly to act the part of the maid Violet doesn't really have, uses her knowledge of Violet's dual identity to extract information from her on one of Violet's friends, whom she wants to seduce and settle down with. Since Fiona and said friend both end up genuinely happy together, Violet doesn't particularly resent this.
- Evil Genius: The current Duke's late father, a famous inventor, had a plan to seize power, although he may have been a Well-Intentioned Extremist rather than outright evil.
- Half-Identical Twins: Despite the whole premise of the book being that the female twin assumes the identity of the male twin, this trope is averted. Violet uses Ashton's name, but doesn't look like him, and the scheme works simply because the people she meets don't know either of them. When the twins are seen together, they're able to pretend to be cousins rather than twin siblings.
- Historical Domain Character: An elderly Ada Lovelace
appears a number of times. Among other things, she identified Violet as a woman at first glance. - Love Dodecahedron: A bit, yes. The Duke loves Violet/"Ashton" (not knowing that they're the same person, and emphasising the former while downplaying the latter since it would be unprofessional and he doesn't consider himself gay anyway). Violet reciprocates. Cecily thinks she loves "Ashton", though eventually decides that she doesn't. Violet's friend Jack and nasty blackmailer Volio both love Cecily, though Cecily initially dismisses the former and doesn't even know about the latter (though he thinks he's had a long and passionate correspondence with her).
- Love Letter Lunacy: When Volio tries to blackmail Miriam into carrying letters between himself and Cecily (throwing in a rape threat to boot), she responds by working with her friends to create fake letters from Cecily, fabricating Cecily's side of a drawn-out "correspondence". Volio is pleased at Cecily's passionate words, though Miriam tells her friends that Cecily would be actually be annoyed that anyone would think she wrote like that. They make sure that "Cecily" tells Volio not to approach her directly for the sake of secrecy, but he eventually does so anyway. The real Cecily's simple explanation that someone's been playing a joke on him, making his whole "romance" with her imaginary, causes him to snap.
- Mad Scientist: The numerous scientists of the cast aren't mad, exactly, but their output isn't necessarily much different than if they were. Some of them are certainly eccentric.
- Maid and Maiden / Matron Chaperone: Assumed by many characters to be the case with Cecily and her governess Miriam, though in fact, Miriam isn't actually very old and is a lot less prim when she isn't under observation. She's in a relationship with one of the senior students and goes out drinking with him and his friends. This causes problems when another student notices and tries to blackmail her into letting him hook up with Cecily.
- Mecha-Mooks: There's an army of these hidden in the basement of Illyria Academy. They're broken out by the villain for the finale.
- Omnidisciplinary Scientist: Illyria Academy seems to train them. All students study physics, chemistry, biology, astronomy, and reckoning (apparently mathematics plus early computing).
- Powered Armor: Violet's big invention works like this. She sees it as benefiting women, since if it becomes common, concerns of physical strength differences between the sexes are rendered moot.
- Real Women Don't Wear Dresses: Played with. Violet's relationship with things stereotypically feminine is somewhat complicated - she starts out ignoring it all in favour of being something of a Wrench Wench, and then disguises herself as a man to attend Illyria Academy, but when she is able/required to change back for a while, she finds she doesn't mind dresses so much any more (although acknowledges that this might just be relief at not needing to conceal her gender).
- Sadist Teacher: Bracknell, the substitute astronomy teacher, seems to consider mocking and denigrating his students to be the only thing in his job description.
- Secret Identity Change Trick: Violet does this at the end, changing from her male clothing/persona to female under cover of her Powered Armor-like machine, but unlike most examples of the trope, she wants it to be obvious that its the same person before and after. It's part of her big reveal, and it's just the actual changing that she needs to hide.
- Secret-Keeper: A number of people know or learn Violet's secret, but the only one permanently at the Academy with her is her friend Jack, who keeps the secret throughout (even when it would be advantageous for him to tell, such as to divert Cecily's attention away from the not-really-male "Ashton" and towards himself).
- Shout-Out: There are numerous references in the story to both Twelfth Night and The Importance of Being Earnest, among others. Particularly quick to be apparent is the fact that Twelfth Night and this book have protagonists named Viola and Violet, respectively, and both disguise themselves as men while in a place called Illyria (a country in Viola's case; a school in Violet's). Numerous characters share names with, or have similar enough names to, characters in one or other of the plays (Cecily, Toby, (Mal)Volio, Earnest, Algernon, etc.), although they are not necessarily in the same roles or with the same characterisation. There are also plot parallels (such as fake love letters to a character called Malvolio in Twelfth Night and one called Volio in this book).
- The Spark of Genius: The previous Duke and his cabal seem to have believed this, claiming that some people were simply born geniuses and some were not (and that the former's natural place is to rule over the latter).
- Sweet Polly Oliver: The central plot is about Violet disguising herself as a man in order to attend a school.
- Sweet on Polly Oliver: Twice. The Duke falls in love with Violet/"Ashton" as a person while being under the misapprehension that they're two people. Cecily, meanwhile, falls specifically for Violet's "Ashton" persona, or at least her conception of it. Once the secret is out Violet and the Duke end up together, although not before the Duke is rather put out at the deception and consequent public embarrassment. Cecily, meanwhile, decides that she was just Loving a Shadow.
- Take Over the World: The current Duke's father seems to have had this as an end-goal. He failed, and had to shut his secret society down and go to ground. However, the lab he sealed up in the basement (and the fact that he gave Volio a key) causes significant problems.
- Unsettling Gender-Reveal: The revelation that "Ashton" is actually Violet comes as rather a shock to the two people romantically entangled with him/her, though both get over it. Violet's non-romantic friends are pretty relaxed about it.
