When Liam dares his classmate Imogen to come on a forbidden tour of the railway tunnel being drilled through a nearby mountain, he hopes she’ll quit protesting about it damaging the environment — his dad is an engineer working on the tunnel, after all. Just as they reach the huge tunnelling machine everything goes horribly wrong. When the rocks stop falling and the dust settles, they are trapped, kilometres below ground, in the dark. Water is trickling in and beginning to rise. And nobody knows where they are. Can they stop arguing and start working together to escape before time runs out?