Rebecca Yarros is notorious for her heart-stopping plot twists, and Iron Flame's ending delivered a massive reveal. By the end of the book, Yarros makes it known that Xaden has a second signet—something that should not be possible based on the laws of dragon bonds. According to the law, no dragon is to bond with a descendant of a previous rider, as this could potentially grant a rider a dangerous second signet. Initially, Iron Flame's twist comes as quite a shock, but in re-reading the series, it's clear this is a plot dynamic Yarros has been teasing the entire time.

It's common knowledge that Xaden's shadow-wielding makes him one of the strongest Fourth Wing characters, but Violet later discovers that he has another one of the most dangerous signets—an Inntinnsic ability to read people's intentions. Given this is an ability that could have had him killed, it's understandable...