Black is The first book part of the Circle Trilogy by Ted Dekker. Has a green cover with the title in Black. Involves Thomas Hunter is an ordinary guy until he gets shot one day because of some money owed, and he is thrown into a new world. He can go back and forth between the two worlds when he goes unconscious, the two worlds become more dependent on each other because they are both coming to the same threat of being taken over by evil. He is the one man that can save both worlds, and he can use his knowledge and skills acquired in world to help in the other. Both worlds start to parallel each other in significance of events.
The end of the book leaves off with Hunter about to come to with Carlos holding a gun to his head.