A Darkling Plain is the fourth and final novel in the Mortal Engines Quartet series written by author Philip Reeve.

The novel won the 2006 Guardian Children's Fiction Prize and the 2007 Los Angeles Times Book Prize for Young Adult Fiction.

The book is set six months after Infernal Devices. Wren Natsworthy and her father Tom Natsworthy have taken to the skies in their airship, the Jenny Haniver. After the apparent death of the Stalker Fang at the end of Infernal Devices, General Naga has seized command of the Green Storm and has signed a peace treaty between the Green Storm and the Traktionstadtsgesellschaft, ushering in a new era of peace and trade. Whilst Wren is enjoying life as an aviator, Tom misses Hester, and has been informed by a doctor that his weak heart means he only has a few years left to live. The Lost Boy, Fishcake, is secretly repairing the Stalker Fang, coming to regard her as the mother he never had. Theo Ngoni has returned to Zagwa and rejoined his family.