Some of the wittiest banter ever - no, not between host Toby Hadoke and special guest, Renaissance man  Gary Russell (who has written, acted, scripted edited, novelised ... in fact there is nothing he hasn't done for Doctor Who). No, writer Chris Boucher makes the dialogue and characters sing but everyone is on form this week so it's a case of what, or who to choose... script, direction, acting, design? Which should be allowed into the special club of best bits?  Well, one thing that won't be is the murder mystery element of the story as it happens. Not with those trousers.