Can we trust Katherine? That was one of the main questions at the heart of "The House Guest."

On April 7, however, the issue will shift to: Can we trust Isobel?

Why is Elena's mother's back? What role will she play in the arrival and attempted dismissal of Klaus? How will she and John continue to work to free their daughter from the Salvatores? Unfortunately, we have many weeks to ponder these questions.

But we also have the following preview for "Know Thy Enemy" to hold us over. You showing up changes everything, Katherine says to Isobel. Hmmm...

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.