'The Darkness Dwellers' is the third and final book released of the Kiki Strike series. Ananka's secret crush is revealed, Kaspar is in it, Oona's "sister" comes back, Betty helps Kiki deal with her horrible relatives and DeeDee is stalked because of a new invention. Spoilers ahead.

On her blog, series author Kirsten Miller stated she had to research taxidermy, bone collecting, code breaking, royal curses, entomology, French insults and etiquette.

The book takes place in France and New York with alternating third-person narrative with Ananka, Kiki, and Betty. Kiki is kidnapped by Sidonia and Livia in France while traveling to Pokrovia. Betty goes to rescue her through Amelia Beauregard's ettiquette school, as Amelia's assistant. The rest of the Irregulars hold down Manhattan and deal with its problems there. Keeping Ananka from falling in love with the wrong man and some stuff involving Oona's evil twin impersonating Oona and getting her in some rough spots.

The plots in France rely heavily on catacombs under Paris that are protected by The Darkness Dwellers, a band of various people not unlike the Irregulars. Unlike the Irregulars, the French police force is aware of the Darkness Dwellers and is a continuing battle to uncover their identities and put them in jail. 

The book was released on January 22, 2013 along with a special surprise for the fans.

The book ended in the possibility of new adventures, with Kiki and Etienne thinking about going to New York together.