Episode was a 6/10 for me, at best. Mary has never been an interesting character. Her reveal as a super secret agent felt like a forced, lazy, out of place "twist" from the get go.
The show has focused entirely to much on her story, which has the qualities of what I can only imagine to be writers going "well what if she was a .... all along!" instead of a deliberately crafted storyline. The contrast to this was Irene: she was interesting from her first scene and they continued to organically build on her established personality. With Mary, the random dice analogy fits her character in more ways than the writers seem to realize and not in a good way.
Not to mention the acting during the death scene was atrocious by everybody involved. I'll watch through the end of this season but judging from s3 finale and this, my expectations are very low.