似乎没有任何征兆的一天,27岁的志村朔美(仓科加奈 饰)突然遭遇严重车祸。当她再度醒来时,发觉自己丢失了过去十年的记忆。此时的她只记得17岁那年12月以前的事。前男友细见良彦(中野裕太 饰)的到来让她满心欢喜,尝试着改变自己性别的高中同学大岛薰(伽奈 饰)也受朔美母亲之托来照顾她。家庭重组,当年美术部的男孩去世,完全不认识的女子恶意咒骂。十年的空白,让朔美兴奋之余不知所措。在良彦和薰的陪伴下,她有意识地寻找失落的记忆,关于爱,关于恨,关于伤心与绝望,有如海水退潮后沙滩上的贝壳,渐次浮现…… 本片根据狗饲恭子的原作改编,岩井俊二担任配乐。Sakumi was seventeen when she had such a car accident that the next ten years of her life are a blank. She lost any recollection of the ensuing ten years. She would like to regain the memories and that portion of her life and has Yoshihiko to help her. Yoshihiko is an old friend and a class-mate who also has feelings for Sakumi.