在一栋大楼最底层甦醒的13岁少女，瑞吉儿·加德纳(レイチェル・ガードナー)，她没有任何记忆，不知道自己为何在这里，而为了回到地面，她开始试着逃出去，但是突然在她面前出现了脸上缠满绷带、拿着有如死神般的镰刀的杀人鬼。 　　“拜托你，杀了我。”“帮我一起从这里出去吧。那样的话，我就会杀了你。”两人之间的奇妙羁绊，随着那“荒诞的约定”而逐渐加深。这里究竟是什么地方？两人为何被囚禁于此？等待着两人的命运又是如何？为了从密闭大楼逃出的抱死觉悟之行揭开了序幕。两人最终是否能够坚守约定，并且安全地逃出这栋大楼呢？13-year old Rachel awakens to find herself trapped in the basement of an abandoned building. Without any memories, or even a clue as to where she could be, she wanders the building, lost and dizzy. In her search, she comes across a man covered in bandages. He introduces himself as Zack and he wields a grim-reaper like sickle. A strange bond is struck between them, strengthened by strange, crazy promises. These two, trapped in this strange building, don't know why fate has placed them there. But they will work together desperately to find a way out.