I think Sherlock is genuinely puzzled by Mycroft's reaction to CAM...
It is an odd reaction , so there may well be a reason why.
He reacts similarly to how he does with Irene and it may be for a similar reason.
Had Mycroft sent Mary in to deal with CAM or did he at least know she was there?
---------------------------------------------------------------------------------------------------------------------------------------------------------------
http://professorfangirl.tumblr.com/post/105838327464/heres-an-outtake-of-mark-gatiss-on-the