Some fun moments and the idea was intriguing but I felt very frustrated by how the characters had to be dumbed down for it to work. There is no way the Great Detective wouldn't figure out early in the episode who is who or that she would drink the tea after Strax told her Evil!Jenny is trying to poison her. And I felt very uncomfortable that one of the most explicit scenes we ever got between Jenny and Vastra is actually between Vastra and a Zygon, and it's played for laugh.