it is accidentally deduced that oxygen in pure form is problematic to the marshmen, and this non-lethal defence is used to force the marshmen out of the starliner. during their retreat, varsh is killed, leaving adric in emotional turmoil. with the marshmen returning to the swamps, the boy stows away on board the tardis. meanwhile, his fellow colonists pilot the craft away from alzarius. the doctor, romana and k-9 are unaware of adric's presence as they leave the planet.