Chains of Iron by Cassandra Clare (Book 2: The Last Hours trilogy)

Cordelia Carstairs is now married to James Herondale—not out of love, but to protect his family from scandal. While they pretend to be a couple, James is still secretly in love with Grace Blackthorn, who has mysterious power over him.

At the same time, London is being terrorized by a series of murders committed by the dead, and Shadowhunters are losing control over their powers. Cordelia, James, and their friends must unravel the mystery behind these attacks and the source of the dark magic threatening their world.

As secrets unravel and emotions intensify, Chains of Iron explores themes of duty vs. desire, trust, and the consequences of hidden truths.