The blurb for the next DS9 relaunch novel, The Soul Key, has been posted on Simon and Schuster's website, this is it:

There is a void in the alternate universe that demands to be filled. Iliana Ghemor, the Cardassian operative who years ago was altered in both body and mind to replace Kira Nerys, dreams of fulfilling a prophecy that will mark her as the one true Emissary of that other reality -- a messianic figure who could lead her followers into an era of renewed hope...or an age of deepening darkness.

Ghemor's claim to the mantle of the Emissary is by no means certain, however, as the inexorable pull of providence tugs also at other souls who are swept into the vortex of the Prophets, the remote and timeless beings who have set these strange events in motion.

But the stakes are higher than anyone imagines: for the outcome of this struggle for the fate of one universe will ripple across many others, and become the key to unlocking a future that will prove to be the greatest trial yet for the heroes of station Deep Space 9.