TPTB seem to believe that no one is indispensible. That's the big difference between Brit and American TV. Watching "Bad Girls" ,it's the same thing. It's like a revolving door of actresses coming and going each season. The question to me seems to be how much shuffling can they do with Spooks before the audience loses it's enthusiasm and interest. You would think that they would want to viewers to be at least somewhat interested in particular characters... :shrug
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To seek out new life and new civilizations. - Star Trek