A tower exists that summons selected individuals known as "Regulars," promising to grant their deepest desires. Whether it is wealth, fame, authority, or something surpassing them all, everything awaits those who reach the summit. Twenty-Fifth Bam is a boy who has known nothing but a dark cave, a dirty cloth, and an unreachable light throughout his life. When a girl named Rachel came to him through that light, his entire world changed. Becoming close friends with Rachel, he learned various things about the outside world from her. But when Rachel says she must leave him to climb the Tower, his world shatters around him. Vowing to follow her no matter what it takes, he sets his sights on the tower, and a miracle occurs. Thus begins the journey of Bam, a young boy who was not chosen by the Tower but opened its gates by himself. They call his kind "Irregulars"—beings that have shaken the very foundation of the Tower each time they set foot inside it.