The Umbrella Man is back. But when the Doctor recruits UNIT's Scientific Adviser Elizabeth Klein for an off-the-books mission to the apocalyptic final days of Hitler's Germany, he isn't expecting Klein's hapless young assistant, Will Arrowsmith, to be joining them too.

The Doctor isn't the only alien creature seeking to loot a very particular secret from a Nazi base in Dusseldorf, however. Strange and sinister beings are converging on the same time/space location in search of the scientist Schalk, whose experiments are the key to a devastating power...

The power of Persuasion.