4. Missing Planets (Series Four)
This one fared a little better than the blandness of Torchwood earlier in Davies' era of Who, because it actually formed the basis of several episodes. Eschewing his previous tactic of repeating a single term over the course of the series, series four introduced several little ongoing mysteries simultaneously; the Medusa Cascade got the occasional mention and sounded suitably ethereal, as did the Shadow Proclamation, ATMOS and the disappearance of bees. However, it was the abundance of disappearing planets that stood as the heart of Davies and Tennant's final full series of Doctor Who. The Adipose breeding planet was the first to go, and that gave Mrs. Foster and her legions of fat babies motive to come to Earth and convert us lot into Adipose. So far, so good a story arc actually having influence over the individual story. Then came The Fires of Pompeii and the wayward Pyroviles were playing the same card as their planet was also gone. All the while, the Doctor fleetingly wonders why the bees have disappeared and that strange old Cascade draws ever closer. Make what you will of series four's two part finale; for some its a whimsical celebration of four successful years of new Doctor Who, for others its a bloated mess of too many plot-threads, redundant characters only present for fanservice and convenient reset buttons abound. At the very least, unlike Moffat's series six head-scratcher of a finale, every element gets adequate treatment and is fully resolved by the end. The Shadow Proclamation is where the Doctor goes to try and work out where the planets have gone, the bees have disappeared because they saw the bad things coming and went home (bees are aliens well, not all of them), the planets have been stolen by Davros and the Medusa Cascade is the galaxy where he has taken them. All present and correct.