BananaClownMan wrote: I think I've cracked it; What is Alt. 12 is the end result of the cliff-hanger of Part 4, when he succeeds in altering everyone's memories and then sends them on their merry way. A sort of bootstrap paradox is you will.
Then, with the mind implant in place, the Doctor leaves Clara after Dark Water and the events of Four Doctors happen. To me, it all fits together.
Anyone else got an opinion on this?
Too much theory, not enough evidence.