No spoilers, just quick comments:
1) I guessed what was in the water about 10 minutes in...
2) I was totally off on who Missy is, but some of you guessed it!
3) That was a rather brutal and heart-wrenching opening scene.
4) Knowing who Missy is now, I'm a little weirded out by her behavior in relation to the Doctor and others.
5) Is Jenna definitely leaving the show? Good. I think it's time.
Enjoy the show!