No. 6.

"With the help of the enigmatic Rat, Shion becomes a fugitive, escaping No. 6 and getting his first glimpse of the desperation and violence that are facts of life outside the city wall. And as Shion learns more about the secret that forced him into exile, his loyalty to the people he left behind and Rat's thirst for revenge threaten to tear the pair apart!"--Page [4] of cover.