It's a technothriller, in which British and Russian intelligence forces clash over a new piece of military technology. It's a comedy. It's set in 1876.
Captain Horatio de la Terre has served in His Britannic Majesty's navy for thirty years, during which time his greatest assets have been a spotless sense of duty and an impeccable poker face that he presents to anything he doesn't understand, which is just about everything. Right now, he doesn't understand why the people of Maldona, where he's stationed as naval attaché, insist on greeting one with a kiss on the cheek; why his superiors want him to study the Maldonan Navy's newest (which is to say, first) ship and report on its design; or why the embassy's information officer is so keen on the idea that it might sink during its seaworthiness trials. He's thoroughly bewildered when a young woman attempts to burgle his office. When the information officer casually suggests breaking his sworn word of honour, he doesn't understand that either, but he does understand that Something Must Be Done. That's when things start to get really confusing...
This novel provides examples of:
- Alternate History: Technically; the military technology at the centre of the story is real, but wasn't actually invented until much later. In the end, it's suppressed, leaving history back on track — then the last two pages unveil the inventors' next project...
- Always Identical Twins: Hetty and Letty.
- Compensating for Something: When Captain de la Terre gets his first look at Maldona's new vessel, the narration notes that this would have been his reaction were he not quite so well-bred.
- Finishing Each Other's Sentences: Hetty and Letty do this occasionally when they're brainstorming an idea.
- I Gave My Word: Captain de la Terre is a man of his word, which is what gets him really enmeshed in the plot.
- Funetik Aksent: A Scottish engineer whose accent is so broad several characters express uncertainty as to whether he's actually speaking English.
- Ironic Echo: The first scene opens with Captain de la Terre having just been kissed on the cheek in greeting by a Maldonan, to his intense displeasure. The last scene opens with Captain de la Terre having just been kissed in greeting by a (different) Maldonan, not on the cheek and to a much more appreciative response.
- It Will Never Catch On: Captain de la Terre's reaction at the end to the next project.
- Let's Get Dangerous!: Captain de la Terre after he thinks Letty has been killed by the Russians.
- Mistaken for Badass: Captain de la Terre gains a reputation as a savvy, dangerous man who never reveals what he's thinking, when most of the time what he's thinking is some version of "I don't understand what the hell's going on". By the end of the novel, he's discovered unsuspected talents and depths, but luck and misunderstandings still account for a large part of his reputation.
- My God, What Have I Done?: On seeing its first use in a real battle, the technology's creators realise the consequences if it becomes widespread, and set about making sure it can never be recreated. They don't indulge in melodramatic rhetorical questions, though.
- Not Using the "Z" Word: There is a word that will almost certainly have occurred to the reader by the end of the first chapter in relation to the technology at the centre of the plot. Nobody in the novel ever uses it.
- Officer and a Gentleman: Captain de la Terre.
- One Dialogue, Two Conversations: Happens a lot, particularly to Captain de la Terre, who spends much of the time out of his depth, but has a lucky tendency to word things in just such a way that he appears to know exactly what's going on. (Or, occasionally, an unlucky tendency, as in the scene where the love interest offers him a proposition he's too much of a gentleman to recognise for what it is, and his response innocently sends the conversation downhill fast.) Notably, he spends the entire novel fundamentally misunderstanding the nature of the technology everybody's interested in, but through the course of multiple conversations neither he nor anybody else realises this.
- Punch! Punch! Punch! Uh Oh...: When Captain de la Terre and the secret agent Reddon are taken captive and are caught escaping, Reddon gives the guard a one-two punch and succeeds only in hurting his hands. De la Terre says something uncomplimentary about his technique and fells the guard with a single uppercut.
- Ruritania: Set in Maldona, a small country east of Greece and west of Turkey.
- Captain Horatio de la Terre bears some resemblance to another Captain Horatio whose opinion of himself is at odds with his reputation.
- The British secret agent, Reddon, is a 19th-century James Bond, complete with evening dress, taste for vodka martinis shaken not stirred, and a mysterious superior called Mr. Emm.
- The technology at the centre of the plot is named after a type of shellfish, just like the Nautilus.
- Spy-Tux Reveal: The British secret agent does a version of the classic tuxedo-under-wetsuit, only instead of a wetsuit it's one of those clunky old diving suits with the metal fishbowl helmets.
- Theme Twin Naming: Hetty and Letty.
- Tuxedo and Martini: The British secret agent, Reddon, ticks all the boxes. He even has a comprehensible excuse for wearing evening dress while breaking into the opponent's lair.
- Twin Threesome Fantasy: Before getting to know Hetty and Letty well enough to tell them apart and develop a preference, de la Terre idly speculates about the possibility of wooing both of them, though being a gentleman his speculations don't get really, you know, personal.
- Wooden Ships and Iron Men: Set in a period where these were already beginning to give way to iron ships, but the tradition is still taken seriously.