When they return, the Institute has been taken over by Centurions, graduates from the Scholomanche, led by Zara Dearborn, who reveals that she is engaged to Diego Rosales.

Meanwhile, Kit, having learned that he is a Shadowhunter named Christopher Herondale, tries to leave the Institute several times, but is dissuaded by Jace and Ty.

When they reach the Unseelie Court, the group challenge the King for a trial by combat for Kieran's release, with Emma becoming a champion.

Back in Los Angeles, Kit, Ty, and Livvy spy on Zara, who wants to take over the Institute and plans to destroy all Downworlders.

The Seelie Queen offers Julian a way to break his parabatai bond with Emma in exchange for retrieving the Black Volume, then asks the others for help to overthrow the Unseelie King.

After getting his first rune, Kit meets the ghost of Jessamine Lovelace and obtains information about Malcolm's former home in England, located in Polperro.

Back at London, Kit, Ty, and Livvy visit the former Blackthorn Manor and find a crystal containing Annabel's memories.

Cristina gets close with Kieran and follows him when he visits his brother, Adaon, to convince him to take over the Unseelie throne upon their father's death.

He tells her that Zara is engaged to Diego so she can take the Rosales family heirloom, the Eternidad, which is currently in Jaime's possession.

She begins dating Gwyn, confessing that she is transgender, which is the reason why she refuses Penhallow's offer to lead the Los Angeles Institute, as she does not want to be outed.

She agrees to testify at the Clave and give Julian the Black Volume, which he takes a copy with his phone, if she is protected by Magnus and given the Blackthorn Manor.

Freaking out, she steals the Mortal Sword and kills Robert with it before engaging in a frenzied murder among the Clave.

As Julian is left to cradle Livvy, Emma tries to follow Annabel but fails, only glimpsing her taking off with the Unseelie King before disappearing to parts unknown.