As a young mouse living in the subway, Nib loves to hear about Tunnel's End: a beautiful yet dangerous roofless world filled with incredible wonders and mouse-eating monsters. One day Nib decides to set off, away from his dirty crowded home, to find Tunnel's End. Along the way he meets Lola, a girl mouse, and together they navigate the long and dangerous tunnel. Just when they have given up hope, they hear a small chirping sound - can it really be Tunnel's End?