The Known Unknown

Brother-Codicier Jensus Natorian of the Blood Ravens has served the Deathwatch for many years, bringing his psychic talents to bear against the hated xenos on countless battlefields. However, when his original Chapter request aid in combating a genestealer infestation within the space hulk Endless Despair, he is compelled to answer this new call to duty in person. Will an unexpected reunion with his old mentor, Librarian Captain Lanneus, on board the hulk herald the beginning of greater cooperation between the Chapters, or something much darker?
Read it because
A Space Marine Librarian turned against his brothers by the power of the Hive Mind? Sounds like a winning read to us.