When it comes to conceptual world-building, Three Dark Crowns by Kendare Blake did well at integrating various core elements of the setting itself, with a few critical misfires that flubbed the ending. Still, the blend of various magics is unique enough, and its effects on the culture plausible enough, that it sets Fennbirn apart from other YA fantasy novels of that nature.
Warning: spoilers abound.

The Six Core Magics
Fennbirn’s magic system is a multi-faceted piece affected by the queen’s bloodline. Three types take the focal point: the poisoners, the elementals, and the naturalists. The poisoners are immune to all poisons, and have an intuitive sense on how to use different toxic plants to harm others. They are based in Prynn, although the powerhouse of the poisoners, the Arrons, are housed at Indrid Down.
The naturalists’ powers are somewhat linked to the poisoners, as their magic has to do with plants as well as animals. Their gifts encourage plants to grow, although they’re best known for their way with animals. Naturalists have familiars, and one’s familiar supposedly says a lot about the strength of their gift. The naturalists are based in Wolf Springs.
Thirdly, there is the gift of the elementals. As the name of the gift implies, they’re able to use the elements around them. Supposedly, elementals favor particular elements, and emotional flare-ups can be seen in gusts of wind or fires growing suddenly large. The true extent of the elemental abilities is unclear, as the most-used elements are wind and flame. The elementals are based in the the holy city of Rolanth.

The other three gifts are much smaller in nature, looked down upon by the others. The war-gifted, stationed in Bastian City, have the ability to sneak up on people, can quickly learn any weapon, and generally have a very high pain tolerance. The seers, located in Sunpool, are essentially clairvoyant. They can read the future in the toss of knuckle bones or through the use of scrying boards, and they can tell where death has been. And, finally, not a traditional “gift,” yet a source of magic all the same, is that of low magic. No one is born with the ability to wield it like the five former gifts, but it is similar to witchcraft, using blood and spellwork to achieve things that the rest of the magic cannot. Queensblood is supposed to magnify how powerful low magic can be. It is stated to always come at a price, although the price is never directly connected to the spell itself, leaving readers with the question of whether or not there actually is a price, or if those prices are simply superstitions connected to real-life consequences to actual decisions.
Limitations of Magic
Not everyone is born with the ability to wield magic. The exact ratio is impossible to determine, as there are only a handful of characters noted to be giftless among the countless characters who have one gift or another. I remember specifically that there was one giftless person on the Black Council, because they mentioned it literally every time she was on the page, and Joseph Sandrin.
For those with magical powers, each person only gets to be in one particular category. There are mentions of the legion-cursed, people who re born with two magical abilities, but they are rare, and supposedly having two gifts make a person go mad, so children displaying two gifts are killed off while young. Jules Milone, best friend of one of the triplet queens, is discovered to be legion-cursed as both naturalist and war-gifted, and it makes her lash out when the curse is broken.
The strength of gifts correlate to the queens’ bloodline. Each queen bears triplets, each with one of the five main gifts. The gift of Sight has become miniscule after a tradition was formed to kill all seer queens, as the Sight made the queens go inexplicably mad. The war-gift is rare in the queen’s line, for reasons unknown, although these queens have ascended before. Usually, the triplets are poisoners, naturalists, and elementals. Whichever queen ascends makes their own gift grow stronger.
Connections to Location, and Religion
The passing down of different magical gifts is left unclear. There are no noted Poisoners in residence at Wolf Springs, and no naturalists in Rolanth, and so on. The exception to that rule is the temple itself in Rolanth, though the temple requires its priestesses to leave behind their respective gifts in service of the Goddess.
Whether that makes the gifts themselves as genetic, or specific to location, remains unclear. It is reminds me of Avatar the Last Airbender, where we’re not really given any examples of firebenders in the Water Tribe, or earthbenders in the Air Nation. In Legend of Korra, the four elements grow more integrated, and so intermarriage gives the child a fifty-fifty chance of gathering one power or the other. Aang’s and Katara’s marriage showcases that, with one air-bender (Tenzin), one water-bender (Kya), and one non-bender (Bumi). There is no such examples to draw from in the Three Dark Crowns series. Only Jules Milone exists as a counter-point, and where her war-gift comes from is never explored. I don’t think her father is ever mentioned.
In the end, the exact nature of each of the gifts remains unknown. It could be that the particular area of the land will give specific gifts to those born in that region, or it could be, like in Avatar, that the characters were so segregated because of prejudices or simple traditions that it was inevitable specific gifts appear in specific locations.
Divisions of Power
The triplets, when they become of age, must engage in a fight to the death. The last one standing becomes the Queen Crowned. This particular practice has led to conflicts and power struggles between the different gifts. The elementals and naturalists look down on the poisoners, especially the Arrons, for their cold-heartedness that stems from their place of power. The last several queens have been poisoners, and so they have grown secure in their position, hence their home at Indrid Down. Conversely, the Arrons sneer at elementals and naturalists as being weak and useless.
Unfortunately for everyone, their seats of power are tenuous. The major families of each gift take in the triplet of that gift and raise them. Of course, when the queen is raised to Crowned, the family that raised them would have the most influence. As a result, Katherine, a supposedly weak poisoner, puts the Arron’s power at risk. Should Arsinoe or Mirabella ascend the throne, then the naturalist Milones or the priestess Luca, respectively, would have the queen’s ear, making the Arrons nigh obsolete.
The Supernatural Threats
There are two specific entities that play a role in the narrative that are not directly linked to the queen tradition. The first is that of the Mist. Created at Queen Illian’s death/murder, the Mist supposedly protects Fennbirn from foreign powers coming with ill intent. It also prevents the queens from escaping the island, although Mirabella overcomes the Mist on multiple occasions, and potential king-consorts and trading ships are allowed through as well.
The mist is described as a horrifying entity. It tears bodies apart, and intentionally turns them around so that they cannot reach their destinations. It kills multiple people as it rises against Fennbirn, and even damages Katherine’s hand in a somewhat foolish encounter she has with it.

The second is that of the ancient dead queens. They were gathered somehow in Breccia Domain, and they can enter a body either when it is weakened or willing. As with many ghost figures, the dead queens can only remain in a “strong” vessel for any length of time, and only a living queen is strong enough to hold them for more than a few days. The dead queens are power-hungry and mad, but they lend the strength and multitudes of their gifts to whoever’s body they are currently in. Their presence allows Queen Katherine, who is considered the weakest Poisoner Queen and is in reality a naturalist of questionable strength, to defeat her sisters, though technically by proxy.
The dead queens themselves act as a threat against the island. The mist supposedly rises up against them, although supposedly the mist rises up to insist an end to the tradition of the triplet queens and the original bloodline. It is unclear, and the exact nature of both are never specified or explored in depth. If the dead queens are supposed to signify the savagery of the queenly tradition, and if the “corruption” in the tradition is supposed to be displayed in the power-hungry nature of the fallen, failed queens, it is never specified in any way to be made clear. All that is said, in the end, is that the mist is vehemently against the dead queens, and, once that threat is gone, the mist does not dissipate, but goes back to its original task, and the dead queens are no longer. Whether Jules Milone, the new queen, will also bear triplets is unclear, rendering the sacrifices made to be more than a little questionable in terms of worth.
Connections to the Outside World
For a country protected by a magic mist, there is an impressive amount of integration between Fennbirn and the “mainland” countries. The mist itself was created as a defense after one of the mainland countries attempted to wage war on Fennbirn. Yet peaceful relations remain. There are mentions of trade, notably after the mist rises and cuts off trade during the events of the novel.
People can also come from those mainland countries, and do, during the ascension years. Young men arrive to court the queens, choosing who to ally them selves with. Traditionally, a queen will choose a king-consort to help her bear the triplets, but beyond that, the king-consorts are not good for much.
In addition, mainland countries for some reason have no magical abilities. If I remember correctly, Billy comes from Centra, and it is to this country that Arsinoe, Billy, and Mirabella flee after escaping Katherine. Their lives on Centra are similar to what one might expect from England in…perhaps the 1800s. Arsinoe and Mirabella both cannot use their powers, not until they’re back on Fennbirn. What makes Fennbirn different from the others remains unclear.
Power Usage–Or Lack Thereof–in Warfare
This is primarily seen in the climactic last battle between Katherine’s royal army and the war-gifted who follow Jules Milone. The battle scenes themselves were chaotic and hard to follow, but it appeared that gifts did not take a prominent role in the fighting.
As is the case with almost all characters who were not the three queens, the use of power in general was rather flimsy. The lives of those who were giftless are not clear. Based on the lack of powers seen in the battle, one might wonder if the giftless were conscripted into the royal army. We see Jules with her legion curse broken once more fighting Rho and the dead queens within her. The fighting there is noisy and its damages were wide-spread. Yet, beyond that, the only gifts we see mentioned are Pietyr’s, when he puts a knife in Billy and later defends himself by saying it wasn’t poisoned, implying, of course, that he had poisoned weapons at the ready for the battle.
It brings up the question of why. Against another army comprised of the gifted, the damage would be similarly catastrophic, but to have an ungifted army, or to have a gifted army that doesn’t use their gifts, seems pointless and illogical. The other explanation is simply that the magic was used, but not clearly described in the battle. A case could be made for either.
Conclusion
Culturally speaking, Three Dark Crowns did an impressive job at cultivating a society that connected to the biggest element of the world-building: the multi-faceted magic system. The cities and families connected to each of the three main magic systems all had their own distinct feel, and, to a certain extent, their own traditions. The world-building would have been more complete by exploring the life of the giftless on such a magic-rich island, and the story would have been more satisfying by a more complete understanding of the supernatural forces at work. The pros and cons contest with each other, leave the story with an intriguing world that fell flat in the end.