199 Wrath of the Zylons part five

Episode 199 Season 40 – Production code 19DWA199 The Zylon war has been dragging on for years. Entire systems have fallen to the destruction, and yet they keep coming. Nothing seems to be able to stop them. The Alliance is desperate, and now a new threat has emerged. One which there seems to be no defense against. No defense, save one. The price they will pay for it, though, will cost them everything. And even the Doctor may find that he has to stand against those he has protected for centuries. Has humanity’s end come? And will the Doctor be the author of it?