The listing, The Devils day!! has ended.
The book is in good condition. Dust cover does have ware.
The Devil's Day by James Blish is about the practice of black magic. He says the information he uses comes from the actual texts but is by no means complete. The book is really a pair of novels, Black Easter which is about the setting loose of a great horde of demons on the Earth, and The Day After Judgement which tells of what happens after they arrive. I find Black Easter to be a good horror story following from traditional Christian beliefs, but The Day After Judgement is rather empty of plot and action, and the characters in it were mostly developed in the first novel. The Devil's Day is the second book of a disconnected trilogy including Doctor Mirabilis and A Case of Conscience. I haven't yet found a copy of Doctor Mirabilis, but A Case of Conscience is a classic novel which can still be enjoyed even if you don't agree with Blish's religious views.
I haven't found any novels by Blish I have disliked, and I particularly liked Cities in Flight, which is really a series of four novellas. The first is about the development of the spindizzy drive which not only moves an object faster than light but creates a force field around itself with a wide radius, and the radius and speed increase with the mass inside the field. By the second part most of the world's cities have installed spindizzies and become interstellar traders, or at least moved away from an overcrowded Earth. After the second, though, the novellas fall to the trend of sequels to become action- and politically- oriented. The rest of his novels are also variations on standard plots and ideas but with strange twists, and considering their age some of them may contain the origins of these ideas. Blish is also well remembered for "Surface Tension", a short story about humans who have been genetically engineered to live in a puddle and their voyages in outer space. "Surface Tension" was featured in the SF Hall of Fame.