Song of Susannah

The sixth volume in The Dark Tower series. 
Song Of Susannah is a pivotal instalment in the epic saga. It provides
the key to the quest that defines Roland's life. In the next part of
their journey to the tower, Roland and his band of followers face
adversity from every side: Susannah Dean has been taken over by a
demon-mother and uses the power of Black Thirteen to get from the
Mid-World New York City. But who is the is the father of her child? And
what role will the Crimson King play? Roland sends Jake to break
Susannah's date with destiny, while he himself uses 'the persistence of
magic' to get to Maine in the Summer of 1977. It is a terrible world:
for one thing it is real and bullets are flying. For another, it is
inhabited by the author of a novel called 'Salem's Lot.