With only three specials remaining before David Tennant hangs up his Chuck Taylors on Doctor Who, anticipation is running rampant for the upcoming Doctor Who special "The Waters of Mars," slated to run this autumn before "The End of Time," the final two-parter in which Tennant's Tenth Doctor will bid adieu to the series. (You can read my exclusive interview with Tennant here .) I had the fantastic opportunity to sit down with outbound Doctor Who executive producer/head writer Russell T. Davies and director Euros Lyn, who directed "The End of Time" (as well as the entirety of Torchwood: Children of Earth ) to find out what they had to say about the end of Tennant's run on the series, which also marks Davies' departure from Doctor Who as well. "The end is on its way now," Davies told me. "There's a darkness descending." Among the topics of conversation: why Davies is leaving the series, what's coming up on Doctor W...