4. There Is A Direct Link Between 'The End Of Time' and 'Time Of The Doctor'
We refer of course to the fate of Gallifrey in the last days of the Time War. Since his return in 'Utopia', the Master has been an integral part of the Time War as the Doctor himself. He was resurrected by Rassilon to be a warrior and to pull the home planet of the Timelords out of the Time War, before he himself was forced back to Gallifrey in its final days. Given the events of 'Day Of The Doctor' and 'Time Of The Doctor', we know Gallifrey is still out there, and with it, the Master. Maybe the Master found an opportunity to break free, escaping onto one of the many Doctor's Tardises as they saved Gallifrey? Alternatively, did he find a way to break though into our universe at Trenzalore, when the Timelords gave the Doctor a new set of regenerations? After The 'End Of Time', the Master seemed trapped on Gallifrey forever, but now we have seen the planet again all bets are off. Time and time again he has demonstrated his ability to survive against all odds - his resurrection saw the 'death' of the Fourth Doctor - and a pocket universe surely won't hold him forever.