Twelve-year-old Luke Smith-Sharma shovels coal under Battersea Power station. He keeps his head down, hoping to one day earn his freedom and return to his family, while avoiding the wrath of the evil Tabatha Margate. When he tries to help new girl Jess, Luke is punished and sent to clean the sewers of the haunted East Wing, a place from which few return.
Whilst serving his punishment, Luke realises he can see things others can't in the Power Station: ghostly things. He befriends a ghost-girl called Alma, who can ride clouds through the night sky and bend their shape to her will.
But when Luke discovers the terrible truth of why Tabatha Margate is kidnapping children and forcing them to work in the Power Station, Alma agrees to help him and his friends escape. Will Alma convince the Ghost Council to help their cause? Will Luke's discovery about who he really is threaten their plans for freedom? And can Luke find his voice, while trying to find a way home?