http://www.digitalspy.co.uk/tv/s7/d...3/doctor-who-exec-john-simm-could-return.html
I personally would have the doctor land somewhere and find out something unusual is happening(Everyone is healthy)
The Doctor then discovers that the master is behind all this but he looks different.
At a recent Doctor Who screening in New York, Moffat suggested that Simm could reappear in a future episode.
"After [his last appearance] he'd been saying, 'I think now that David [Tennant]'s left as the Doctor, I would have to leave the Master'.
I personally would have the doctor land somewhere and find out something unusual is happening(Everyone is healthy)
The Doctor then discovers that the master is behind all this but he looks different.