3. Christmas
In each episode, there has been a mention of Christmas. The Doctor tells the Daleks that it is Christmas when they have him in the parliament in the first episode of the season. In the second episode, Rory says that he does not have a Christmas list, but The Doctor exclaims that he does. And most recently, The Doctor wondered if someone had been peeking at his X-Mas list while walking into Mercy. This is possibly our biggest clue. The way I see it, the season will end with the newly hatched Master teaming with the Vashta Nerada and force Santa Claus to deliver only eggs and faulty light bulbs this Christmas. And it will be up to The Doctor to save Christmas.