by James Blish
Reading history and reviews
Finished in 2006I picked up this and The Day After Judgement after a conversation with a colleague at work, who told me that he had recently bought a copy of "Cities In Flight" by the same author. I read "Black Easter" when I was a teenager but not the sequel, until now. I love this sort of detail-oriented science fiction (it's ostensibly about an arms dealer who hires a modern-day black magician to let all the demons out of Hell for one night, and the ultimate consequences) which also asks some serious questions about man's relationship with good and evil, and it was satisfying to finally read the second novel so many years later.
Since there is so little information about the books on Amazon (I think that they are currently out of print), here's a link to the part of the Wikipedia entry on James Blish: http://en.wikipedia.org/wiki/James_Blish#After_Such_Knowledge.