Rosie Cartwright - spoilers

The one thing I really don't get about this series is why they felt the need to write out Rosie Cartwright twice. She goes to Australia in order to have some adventure - this is all well and good, and it's nice to think that when someone is written out of a series, the character has a happy ending.

But then we have the Australia episode. The actress does not appear in this episode, we only discover that she has been murdered by a serial killer. I mean, what's the point? She was already out of the series, why make an episode just to declare, "she's not only gone, she's DEAD and gone". The decision to do this to her is just baffling to me.