Simon R. Green 
Moonbreaker 

From the author of the Nightside series Eddie Drood has finally cornered his archenemy after searching the galaxy end-to-end. But before Eddie can strike, Dr. DOA strands Eddie and his girlfriend, Molly Metcalf, in an alternate universe where the Drood clan have been systematically murdered.The key to their escape lies in this dimension’s eerie and abandoned Drood Hall. Among the ruins, Eddie and Molly discover a mysterious creature who may be able to help them get home in exchange for a favor only a Drood could honor. But Eddie must move quickly if he’s to put a stop to Dr. DOA definitively-all the while reckoning with the fatal poison spreading through his body.