The 20th Century Boys saga begins in 1969 when a young boy named Kenji and his friends write The Book of Prophecy. In the book, they write about a future where they fight against an evil organization trying to take over the world and bring about Doomsday. Years later in 1997, a mysterious cult being lead by a man only known as Friend has emerged and gained strong influence over society.
A series of catastrophic events begin to occur, mirroring the prophecies made up by the young Kenji. The greatest fear is that the climax of The Book of Prophecy will become a reality: on December 31st, 2000, a terrifying giant virus-spreading robot will attack the entire city of Tokyo, leading to the end of mankind. The only people who know about The Book are Kenji and his childhood friends. Who is Friend? Will Kenji and his friends be able to save mankind and live to see the 21st Century?