Vallahan is an "ancient, mountainous Fae territory across the northern sea" from Prythian. It has been "both enemy and ally to Prythian in different historical eras." The country has a "hot-tempered king and proud people." It is a snowy and cold country.
After the War five hundred years ago, Vallahan seized a considerable amount of land.
Ianthe's father was one of Tamlin's strongest allies in the Spring Court and a captain in his forces. Her father sensed the trouble that was occurring in Prythian and fled from Amarantha's rule. They lived there for fifty years, and returned only afterwards, when the harm and death was over. 
Mor repeatedly visits Vallahan as an emissary of the Night Court in an attempt to convince them to sign the peace treaty. Vallahan is resistant to peace because they want to expand their territory. The Queen of Vallahan asks Mor what the point of a peace treaty is when another war might be coming.
- It is possible that the name Vallahan is a reference to Valhalla. In Norse mythology, Valhalla is enormous hall located in Asgard, where many people who have died in combat reside. 
- A Court of Mist and Fury (Mentioned only)
- A Court of Wings and Ruin (Mentioned only)
- A Court of Silver Flames (Mentioned only)
|Characters||Vassa · Demetra † · Briallyn † · Andromache † · Unnamed Queen · Unnamed Queen · Unnamed Queen · Queen of Vallahan · King of Vallahan · Ianthe †|
|Locations||Scythia · Mortal Queens Palace · Vallahan · Montesere · Rask · Neva|
|Characters||Ianthe † (former) · Ianthe's father (former) · Ianthe's mother (former) · Ianthe's sisters (former)|