What is the main conflict in The Dark Tower VII: The Dark Tower by Stephen King?

The Dark Tower VII: The Dark Tower is a fantasy novel by Stephen King, and the seventh in the Dark Tower series. Jake Chambers, his billy-bumbler, Oy, and Father Don Callahan storm the Dixie Pig restaurant in New York City, fighting vampires to free Susannah Dean. Callahan gives himself up so Jake can get to Susannah, who was taken by the low men along with her alternate personality, Mia. Susannah and Mia started out in the same body, but now Mia is her own being and is pregnant. Susannah watches as Mordred, a human who can morph into a spider and is the son of Roland Deschain and the Crimson King, is born. After wounding Mordred, Susannah escapes and meets up with Jake and Oy.