Warbreaker tells the story of two princesses, Vivenna and Siri. Vivenna was contracted through treaty to marry the God-King of rival nation Hallendren. Instead Siri is sent to meet the treaty. Vivenna then follows to Hallendren in hopes of saving Siri from her fate. Both sisters become involved in intrigues relating to an imminent war between their home nations of Idris and Hallendren.