A pre episode of Doctor Who has been written by Peter Harness and starring Ingrid Oliver and titled the Zygon Isolation. It was shown before the watchalong of Zygon Invasion and Zygon Inversion. The next watchalong will be the Fires of Pompeii, which stars David Tennant plus the Doctor before he was the Doctor Peter Capaldi and the Companion before she was the Companion Karen Gillan.