Dark Tower: Treachery (Dark Tower: Treachery #3)

The evil wizard Marten Broadcloak secretly visits Gabrielle, the disgraced wife of Steven Deschain, ruler of Gilead. He subtly manipulates her into agreeing to murder her own husband for him. But there is another mysterious figure with the same intention, so it will take all of Steven's considerable prowess to survive the threats. Meanwhile, his son, the young gunslinger Roland, continues to stare blankly into the magic sphere called Maerlyn's Grapefruit. And the things he sees are not for mortal eyes.