59: Dark Tower 6: Song of Susannah, by Stephen King.

Book 6 of the Dark Tower. Song of Susannah is refreshingly short after the last two monsters, but it sets a punishing pace, with the ka-tet split into three parts. Susannah has been spirited away by Mia, the Mother of her demon pregnancy, taking Black Thirteen to servants of the Crimson King, while Roland and Eddie have been flung after Calvin Tower to save the Rose, and Jake, Oy, and Callahan are following Susannah to the Dixie Pig far in the future. All three sub-plots are moving along steadily, with new revelations at each turn.

This is another one of the books that I quite like. It has a few doubtful plot points - for one, Stephen King is a character within his own novel, which is simultaneously very arrogant and also a necessary part of the story somehow. If the Dark Tower spans all worlds, and given that several of the characters come from worlds that are already very similar to ours, it does make sense that there'd be a number of Stephen Kings in those novels, and that the Stephen King in the key world, as the author of the stories that are, in some form, one of the Beams, would be a key player.

We learn that Walter was the one that offered Mia her Faustian bargain - mortality in exchange for the chance to bear and raise her chap, and that he is Sayre's overlord. Beam-wise, we are told that Fish and Rat anchor ends of a Beam.