In the Doctor Who season 8 episode Time Heist, the team of bank robbers find a case of 6 small items. The Doctor initially claims not to know what they are; when Saibra accuses him of lying, he admits to knowing they are an "exit strategy of sorts". He later reveals they are disintegrators, offering Saibra and Psi
quick and painless deaths rather than having their brains melted by the Teller.
Later still it is revealed that
they're actually teleportation devices,
which seems to surprise the Doctor as much as Clara when they discover
Saibra and Psi are still alive.
So did the Doctor actually believe they were disintegrators or did he know what they really were all along? If the former, why did he 'recognise' them as such
(and why was he so detached after Saibra 'died')? If the latter, why was he so surprised later on? Neither quite seems to make sense.
For those of you who can access it (those in the UK?), the episode is available on BBC iPlayer here.