Grahame-Smith is also the author of enormously successful books Pride and Prejudice and Zombies and Abraham Lincoln: Vampire Hunter. Like those two books, Unholy Night is the re-telling of an oh-so-familiar tale.
It's the story of Balthazar, a thief by profession and wise guy by preference, and his adventures during the 1st century AD. Balthazar runs into a little trouble with Herod's soldiers, gets thrown into prison, and meets up with a couple of other career criminals named Gaspar and Melchyor. After their resourceful escape from execution, the trio meet up with a newly-married couple and their new-born son, and help them escape from Herod's forces who, for some reason inexplicable to Balthazar, are routinely slaughtering all the Jewish boy babies in the area.
Get the picture?
It's a clever idea, and adequately carried out. I can't say there's anything especially noteworthy about the execution, however. Grahame-Smith is a pretty decent writer. I was really impressed, for example, with the way he seamlessly blended the zombie scenes into Jane Austen's prose in his better-known work, and I understand that he did pretty well with the archaic style of Abraham Lincoln's "secret" diaries. (Haven't read that one yet.) But here, he's writing, presumably, in his own voice, and I can't honestly say I'm all that impressed. It's a quick read, and altogether understandable, but his writing's a little more expository than I would like. Still, it's a fun read, and it won't take you long to finish.