I've finished off The Drawing of the Three, and have moved into The Waste Lands.
After picking up Eddie, Roland has gone through the second door and picked up Odetta, a black woman from 1964 whose legs were cut off when she was pushed in front of a New York subway train. She is damaged in other ways, too, and this plays a key role in the story of the third person Roland must meet. I'm not going to give that part of the story away -- suffice it to say, that King pulls some unexpected rabbits out of his hat. (Eddie also makes reference to having seen the movie version of The Shining. I'll save that piece of info for later.)
By the end of the book, Roland and Eddie are joined by a "new" companion, Susannah, and the story segues into The Waste Lands. It seems that at the end of Drawing, Roland may have prevented the death of Jake (the boy from The Gunslinger that Roland had to sacrifice) in our world. This creates a paradox, of course, since if Roland had saved Jake, Jake would never have been drawn into Roland's world and his quest would have ended.
This fact doesn't seem to be sitting well with Roland. And since the first part of the book is called Jake, one suspects that something is up.