It is February 2009, and snow has begun to fall on Kitasanriku and will continue on til May. In school, Isono-sensei is announcing the results of those who passed the qualification exam. He calls on those who who failed ("The rest has passed!"). Aki is unaware since she is listening to the portable music player Santa-san had given her. "Huh? What about me?" "You passed, too." "Jejeh... I did it~!!" She runs off leaving Isono-sensei's class without permission.
潜水士の資格試験に合格したアキ（能年玲奈）は、さっそく種市（福士蒼汰）にデートを申し込む。しかし、種市の返事はそっけない。そのころ、町は北鉄の存続問題で揺れていた。ユイ（橋本愛）の父・功（平泉成）によると、市長が赤字続きの北鉄を廃線にしようとしているのだ。大吉（杉本哲太）らは起死回生の策で「お座敷列車」のイベントを企画。アキとユイを列車に乗せて歌を披露し、観光客を集めようと考えるが…。
