Madness of the Horde King is the third instalment of the Horde Kings of Dakkar series. It follows Davik, which had been mentioned in the previous book, who is considered as "The Mad Horde King" by the others. Compared to the previous ones, it is slow-paced and while there is more action/plot, it still feels like nothing is actually happening. Technically, this alien romance can be still read on its own but I would advise you to read book 1 (Captive of the Horde King) and book 2 (Claimed by the Horde King) prior as there are returning characters whose motivations are based on their stories in the previous books, so having that background information is helpful.

The following review might contain spoilers.

PLOT
Vivienne "Vienne" is a Ghertun slave and gets sent to the Dakkari's main capital as a messenger with an ultimatum, which is unbearable for the Dakkari. Before reaching the palace, she meets the Mad Horde King (Davik) and while they have an instant connection, he lets her go when guards stumble upon them. The instant connection, and attraction, are the reason why he claims her/takes her with him to his horde - though he does so under false circumstances. During the few weeks that she spends with him in his horde, they grow much closer to each other until the past, and all their secrets, come biting them in the ass. To save Vienne and her family, both have to make difficult decisions.

Despite the larger story arc, the entire story is extremely slow-paced and drags on. Partly, it's very boring because there isn't much happening although the stakes are high. A lot of things happened either in the past or off-page, which doesn't help with the boringness.

WORLD-BUILDING & MAGIC
It plays on the planet Dakkar (the position in the solar system/in the universe is never mentioned) as in the previous two books. By now, I would love to have a map to have an overview of where the capital city is, where the Dead Lands are, and where each horde roams. There's not much new input in terms of the planet and the Dakkari society/history aside from the heart stones of their Goddess.
In terms of information about the human population: the timeline of when the old Earth colonies, and Earth itself, become inhabitable due to wars etc. becomes more and more muddled. I thought that I had a good idea on the timeline after the first two books but Madness of the Horde King throws all my perception out of the window. The war that destroyed the colonies (on other planets) seems to be so recent that French is still known as Vienne's family (on her mother's side) uses French terms of endearment (mon coeur, ...) and Vienne was named after a family member. (Funnily enough, her siblings don't have French names.)

As for magic: I suppose that the spirit world, which starts to make an appearance, could be considered as magic. Vienne can sense emotions and during the story, her powers become more pronounced to the point where she can influence/control others (giving commands, ...). Davik and her can also see the spirit of the dead - Which is why Davik is considered as mad as no one else can see them. - and can talk with them when they are awake but also sleeping. In addition, the Dakkari have a story about a sorceress that destroyed an entire horde, and the story influences the perception of Vienne due to her hair colour/general colouring (faintly like an albino, minus the pink eyes).

CHARACTERS
As mentioned, Vienne and Davik are the main characters. There are several side characters (though by far less than in the second book) that either make a reappearance (like the horde kings from book 1 and book 2) or are new side characters (Davik's second-in-command, an old female Dakkari, the Ghertun, Vienne's family, Davik's dead twin). Compared to the previous books, the focus is mostly on the main characters and Vienne doesn't develop a healthy friendship with someone else in the horde.

Vienne is ... annoying. While I know that the "weak but beautiful female" is the trope for the book, she got on my nerves with her behaviour because she feels particularly weak. Due to her gift of sensing the emotions of others, and being able to influence them/to control them, she suffers from headaches and other physical ailments. Aside from the weakness, she is shy, gentle, often enough scared of everything and everyone, and tends to withhold the truth or even lies to Davik because she either mistrusts him or doesn't want to hurt him. I'm not overly fond of characters who tend to do this.
Davik is the typical alphahole and I found him annoying. He's extremely aggressive, lusts for blood, and is an asshole in general. His "madness" stems from being able to see the spirits of the dead, which haunts him as he doesn't understand it and considers it as a curse. However, he plays into the perception that others have of him while he can be caring for his horde in his own way. Similar to Vienne, he lies to Vienne and keeps the truth from her. A lot of his behaviour is influenced by his past trauma as he witnessed the death of his parents, the death of his sister, and was afterwards sexually and emotionally abused, as well as raped, by an older female Dakkari when he was still a minor. If someone needs therapy, it is him.
Concerning his "madness": I have to admit that the previous mentions of him in book 2 created an image of him as a psychopath in my mind. Cold, cruel, brutal, ... - when his madness stems from untreated trauma and abuse as well as the lack of understanding of his gift. Plus, "I like killing too much", which is never shown on-page. There are hints of it in two scenes but I would have expected more/worse?

ROMANCE
Their entire romance is very much insta-love and insta-lust (although the "fated mate" moment that was happening in the first two books is missing). There's no chemistry between them in my opinion and unlike Nelly & Seerin, there's not even an actual development of a romance between them. He just wants to jump her bones right away, she's utterly scared of him but gives in pretty quickly and that's it. Afterwards, it's just insta-love/obsessional love but nothing else. The only hint of some feelings appears in the last chapter.

As for their sex scenes: the sexual tension is there from pretty much the first few chapters. Overall, I would rate their scenes with 🌶️🌶️🌶️ because they tend to be graphic and explicit enough. Plus, there's the element of voyeurism (they watch another couple that doesn't know about them being there), which wasn't really there in the first two books.

TWs & CWs
For the general trigger/content warnings: slavery, past off-page branding, general violence, general sexual content, blood, threat of death/dying, hunger/starving, poisoning, withholding an antidote to the poison as punishment, fantasy racism, wanted pregnancy, mentions of rape (for one side character) and past rape of the MMC as a minor, sexual and emotional abuse in the past of the MMC, spirits/ghosts.

For the sexual content warnings: voyeurism, oral and vaginal sex, fingering, vibrating knot, light choking/BDSM.

TL;DR
A slow-paced alien romance that is mostly based on instant love and attraction with lots of sexual tension and content. The characters tend not to trust each other, which results in secrets and lies. A lack of plot (despite looming large stakes) and only a few world-building information. Davik needs therapy, asap.