*With thanks to our listener Paul McEvoy for the title suggestion

It's the darkest day, the blackest hour. Chin up, shoulders back, let's see what Ben and Mark are made of as they tackle the existential horrors of 'Dark Water' and 'Death in Heaven'. 

Under discussion: How careful do you have to be when dealing with death and real world tragedy in what's ostensibly a family show? Whose internal conflict was greater this series - the Doctor's or Steven Moffat's? And most pressingly of all, what is all of this for? 

After that they squelch their way through Malcolm Clarke's synth soundtrack to discuss another Master plan - 1972's The Sea Devils. Under discussion: nudey monsters, the refinement of Roger Delgado, 70's electronic music and larking about with the Navy.