10 Doctor Who Problems That Time Travel Would Have Solved
9. Warn Someone About The Cyber-Army!
Nightmare in Silver is Neil Gaiman's second script for Doctor Who, following the phenomenal episode The Doctor's Wife. He was tasked with making the Cybermen scary again, which to a large extend he managed. Nods to classic series appeared as the villains were redesigned, which they so often were in the original run yet had remained consistently the same since the revival.
However, an entire army of Cybermen hides under the theme park, waiting to begin their attack and assault on the universe. The Doctor manages to overcome them, though not without difficulty. Only the last-minute intervention by Emperor Porridge saves The Doctor, Clara, Angie and Artie from certain death. Gladly reinstated in the TARDIS, The Doctor flies away, glad to be alive.
He literally has the means to go back and warn the Punishment Platoon of the army that lies in wait under their feet and does nothing. When it comes to The Doctor, sometimes it is the inaction that is the true mark of villainy. He had been fused with the Cyberiad, a shared consciousness of the Cybermen. While defeated, it is entirely possible that it steered him away from warning those doomed souls.