Argent is a Basilisk, someone who was fed poisons from birth to make them immune to all forms of toxin, making their very touch deadly and turning their hair silver. They were then sold as assassins and food tasters, after which they were usually killed.
He himself was bought as a boy by the King to serve as the young Princess' taster, and was seen as nothing more than a tool. She however saw a playmate and dining partner, and a budding friendship emerged.
When Argent was later freed by the Princess, he vanished from her life, only to reappear years later as a skilled healer and apothecary. The Princess, now 16 and a bit of a Tomboy, hears of his return, breezily declares him the Royal Apothecary and sets him up with a new shop.
As they interact and renew their friendship, their growing feelings for each other are complicated by her royal position and his inability to touch her for any length of time.
The stage is thus set for a story of royal politics, unfulfilled love, herbalism, chemistry, and learning; these characters love to learn. Whether it's a prince parlaying a love of insects into a dye industry for his ravaged country, or Primula learning that etiquette may mean the difference between making an ally or an enemy of a visiting dignitary, they grow as people by teaching, doing and being taught.
This series provides examples of the following tropes:
- Action Girl/Tomboy: Primula would much rather practice her fencing or get into adventures than study etiquette. Rumour gives her the nickname "The Princess of Steel", and people are surprised when they see she isn't a rippling Amazon. Later, she learns that her actions reflect upon the kingdom and applies herself to projecting the proper queenly attitude.
- Arranged Marriage: Princes of neighbouring kingdoms court her, and Primula's father wants her to marry for political reasons. She nearly went through with one, but the young prince she was marrying stopped the ceremony.
- Author Appeal: Subverted — the author was a pharmacist before she got into manga. She'd resisted doing a series based on pharmacy because she knew what it was really like, but had run out of ideas.
- Bloody Murder: In one story, Argent uses his blood to eat through the wall of a dungeon. Maybe he's part Xenomorph.
- Green Aesop: The neighbouring country prospering through the use of pesticides. Then coming down with a mysterious illness as the pesticides work their way up the food chain.
- Grey-and-Gray Morality: All the political manoeuvring between kingdoms mean that feelings and morals are sometimes told to sit outside while the adults talk.
- Lethal Chef: Primula is a can-do kind of girl, but her cooking rivals Akane Tendo's. After much practice, her soup levels up to "edible".
- Manipulative Bastard: The King of Beazol is cold-hearted and ruthless, utilising threats, force and the occasional Batman Gambit to come out on top of the situation; he has to be to ensure the survival of his small country. He'll often arrive at the end of another of his daughter's escapades to patch things up and/or claim it was planned that way. He loves his daughter, though.
- Serious Business: Drugs, chemicals and herbs can bring down, or lift up, entire countries. This is Truth in Television, mind.
- Standard Royal Court: Beazol's royal court is rather small, as it's a small country.
- Unequal Pairing: Argent is a freed slave and Primula is the heir to the throne. Beside all the other problems, her father isn't keen on them getting together.