Roland, the last gunslinger, is mortally wounded on an endless beach on a dying world. He discovers a portal to another world which is the first of three doors that lead into the minds of people from this world. The Three will ultimately help him on his quest for the Dark Tower - The Prisoner, The Lady of Shadows and The Pusher.
I'm starting the third volume, The Waste Lands. The back cover reads:
Through time and waste and divided dreams, the last of the gunslingers turn their faces to the Turtle and travel the path of the Beam. And come, when Eddie unlocks the key from the branch and Roland gives the promise he may not keep, to the Drawing of Jake, the undead boy who is one of many who are one... Bound together in thought and treachery, pursued by the Ageless Stranger, they face the perils of Lud and the Tick-Tock Man to reach the Cradle of Blaine the Mono, who is truth and danger and will ransom their lives for a riddle.
And still the Dark Tower beckons, where death lies in the heart of the rose...