"This is called The Bootstrap Paradox. Google it."

So now we have to do some homework before settling down to our favourite programme?

Maybe not, as we get an explanation of what's going to happen before (and after) we watch it happen in Before the Flood. Oh for the simpler if more claustrophobic pleasures to be found Under The Lake.

And our pre-titles primer also involves the fourth wall of the TARDIS being demolished and the Doctor turning his amp up to 11 (again).

So Jim and Martin marshal together their views on what turned out to be very much a game of two halves - and even manage to do so without uttering the dreaded 't-w' word.

And the lads close with a decision of which Tegan's Aunt Vanessa would have been proud.

Uncover (some of) the mystery here.