The Soul Key is a Star Trek: Deep Space Nine novel by Olivia Woods, published by Pocket Books in 2009. It is a continuation of the narrative in the so called DS9 relaunch series and brings to a conclusion the Iliana Ghemor/mirror universe story arc begun in the Worlds of Deep Space Nine novels "Bajor: Fragments and Omens" and "The Dominion: Olympus Descending", and continued in Warpath and Woods' previous novel Fearful Symmetry.