Chain of Iron was published in 2021. It follows the so-called Shadowhunters, a group led by Cordelia Carstairs (who is set to be married to a man she had courted for some time), which investigates killers in early 1990s England. At first, they think that their investigation will go easily. However, they quickly discover that their investigation will be much harder than they had thought. Cordelia's fiance, for instance, has been drawn to the evil forces surrounding his grandmother. Cordelia has also sworn to be an evil force that wants bad things to happen to the world. These things and other barriers that pop up along their way hamper but never stop their investigation, which ultimately leads to them finding the killer and bringing him to justice.
Chain of Iron is the second novel in Cassandra Clare's The Last Hours/Shadowhunters trilogy, which began with Child of Gold in 2020 and ended with Chain of Thorns in 2023. Before writing Child of Gold, Clare planned to write three Shadowhunters novels. Chain of Iron naturally serves as the second act of the story she sets out to tell.
Like her previous novels, Chain of Iron received positive reviews from audiences and publications alike. In their glowing review of Clare's novel, Kirkus Reviews opined, "Fans will sail through and clamor for more [material from Clare]." Other critics felt similarily and cited the novel's eminent readability and interesting prose and characters as a reason for its success.
