Nib is a subway mouse. As a young mouse, he loved to hear the stories about Tunnel's End: a beautiful yet dangerous, roofless world. One day, Nib decides to set off, away from his dirty, crowded home, to find his dream. Along the way he meets a girl mouse named Lola, who joins him. Together, they navigate the long and dangerous tunnel, until, one night, when they have almost given up hope, they hear a small chirping sound. . . it is Tunnel's End, more beautiful than Nib ever dreamed.