I found this week's episode to be rather daft. The basic premise was just too much for me to suspend disbelief. I actually quite liked the recent two-parter about the Zygons, even if the allegory was rather forced. The Goodwin box ending was pretty awesome IMHO. But yeah, this week's episode felt like a massive let down after that.

I think the only logical way to explain the plot would be...
Pulvis ex oculī! "Dust in the eyes"