I take it Elijah dies in Ep 15 and so Katherine is free and they need to find a way to make the manwitches trust them and agree to work with them as the deal is off...

And it sounds like Katherine moves into the Salvatore mansion and is the "house guest". I have visions of her taking turns going into the brothers' bedrooms to annoy them.

Ep 216 is the one before the mini hiatus, right?