Every performer the series billed in its cast list across its nine seasons, from 2003 to 2012. That is the whole rule, and it takes in twenty-one actors, from the top of the cast list to the bottom of it. The large recurring and guest company is out, however well you remember them, however many episodes they turned up in. The answer is always the actor, never the character. A surname on its own counts, and where a performer was credited under more than one name over the years, either name counts. Nothing in this set gives away the story: no question, clue, option or answer tells you how anyone's story ends, and nothing anywhere tells you which seasons a performer was in.