在这部最后一枝蜡笔剧情/家庭片中,中國內地來的婷、熙兩姊弟和歡以及從美國回流的Kathy及香港本地的福嵐「偵探」，都是小學合唱團團友。在一次午膳過後五人食物中毒入院，一同食用過婷媽媽帶來的炸豆腐頓成疑點。大家決定藉一個中國山區交流團，前往豆腐的原產地，嘗試找出食物中毒的源頭。
在交流的最後一天，五人迷路被困山中，飢困交迫，意外發現Kathy的蠟筆可燒成蠟燭，帶來希望。蠟筆不斷熄滅，生存的機會漸減，直至最後一枝……
除非，有一人願意犧牲。
Five elementary school students join the choir:Ting, Hei her brother and Fun are from Mainland China; Kathy is returning from L.A.,and the 'detective' Nam is a Hong Kong local. Hospitalised after food poisoning, the suspect points to the tofu brought by Ting's mom. Incidentally the destination of the choir's visit is the tofu production base. During a field trip, they get lost in the rural hills and have to face hunger, fear and death. By accidental they find out Kathy's crayons can be burned as candles---their only hope. But as the crayon sticks dwindle away into the night, it becomes clear that if all were to survive, one of them has to make a sacrifice.....
