Darker Stars explores the often contentious subject of Planet X. Building upon the historically hot-and-cold hunt for an additional planet in our solar system, the author examines the recent resurgence of scientific interest in this subject, in the re-branded form of Planet Nine. The elusive nature of this object provides the impetus for a hypothesis about planet building in interstellar space, and associated phenomena. In particular, free-floating planetary mass objects and sub-brown dwarfs exemplify the anomalous new characters shaking the foundation of the classic star/planet boundary. Our solar system, too, is full of anomalies, strongly implying the presence of another massive planetary body. As our understanding of dark bodies in interstellar space builds, the author argues whether the existence of Planet X-type bodies should now be considered the new norm. With over 100 images and sources, approximately 500 references, and an extensive index, Darker Stars provides a robust and scientifically-based study of the re-fashioned outer solar system. It is 376 pages in a 6X9 paperback format.