The trainees are heading for a lesson with Dunbar in the training yard when an underground tunnel catches Koko's eye. She wants to explore it but Vee says she isn't ready yet. When no one is looking, Koko decides she's going to see where that tunnel goes, but ends up coming off the tracks.
Elenco: Sacha Dhawan , Imogen Bailey , Andy Nyman , Paul Dodds , Steve Devereaux , Dai Tabuchi , Edward Sharpe , Toby Davies , Warren Clarke , Colin McFarlane , Brigid Harrington .