Countdown to 60: More Daleks!

More Daleks in the third of this series. Significant things will tend to happen in their stories.

In the closing seconds of the episode World's End, a Dalek glides up from the depths of the River Thames.

For the first time the series had revisited an element of its own past. It is where Doctor Who really begins to develop a mythology.

We already had a story arc - the efforts of the Doctor to get teachers Ian and Barbara back to late 20th Century London. In doing so, we had seen a series of unrelated adventures on alien planets or in our planet's past.

Now we have the inhabitants of one of those alien planets return to threaten the Doctor once again - and this time they have come to invade us. The Daleks become the first recurring monsters, in the series' first ever 'Invasion Earth' scenario. The universe isn't infinite - the Doctor has started to have further meetings with alien races and individuals. We'll begin meeting the Daleks on a regular basis from now on, and lots of other races start queuing up to invade the Earth - so much so that the Doctor will eventually have to be based there for a while...