Yanluo became bent on revenge on Ke Wen Yu after she exterminated a nest of Yanluo's demon litter in Lijiang. When Yanluo found a weakness in the wards of the Shanghai Institute, it burrowed its way under the walls and killed all the guards so they couldn't alert the Clave.
Yanluo tied up Jem's parents and made them watch while it tortured their twelve-year-old son by injecting demon poison into his veins, causing him immense pain and hallucinations, and eventually addiction to the yin fen. After a few days, Ke Wen Yu and her husband, Jonah, were dead, and Jem was in a very bad state. By the time the Shanghai Enclave decided to investigate the Institute's silence, Yanluo had left.
Two years later, when Jem was fourteen, Yanluo was finally found and slain.
- Clockwork Angel (chapter 15)