At the start of Stephen King's ''The Dark Tower VI: Song of Susannah,'' there's no synopsis to remind you of the backstory. ''By the time you get to Six,'' says EW's back-page columnist, referring to the second-to-last entry of his epic, ''It's just f---ing ridiculous to try and sum up what's gone before.'' In other words, start with Book One if you're a newbie. But for fans, ''Stephen King'' not only pops up as a character in this one -- he also stars in a helluva cliffhanger, which King promises will be explained in the final ''Dark Tower'' book, due in September. In the meantime, he'll be cowriting a nonfiction book with novelist Stewart O'Nan about the 2004 Boston Red Sox. And he's also started a new novel: ''I don't know how well it's going, but the nice thing about it is, having announced my retirement, I don't feel like I'm under any pressure.''