Season 09, Episode 08 – “The Zygon Invasion (2)”
The future of planet Earth is sealed in a box in Unit’s back archive, and only the Doctor knows what’s inside. With Unit under Zygon control, and Clara lost, the Doctor and Osgood find themselves fugitives in a London where no one can be trusted – but the wily old Time Lord knows there is one last hope for peace. Because that box in the black archive isn’t any old box. It’s an Osgood Box!