6. Torchwood
BBC/Starz
Episode: The Blood Line (2011) Over its first three series, adult Doctor Who spin-off Torchwood went from strength to strength, garnering its own fanbase separate from its parent series. With this is mind, it was shocking when, after its Anglo-American fourth series, Torchwood was put on indefinite hiatus due to showrunner Russell T Davies wanting to try other things. The result of this meant that some loose ends were left untied. Forming one long story, the 10-part series, subtitled Miracle Day, saw the entirety of the human race become immortal - and the usually unkillable Captain Jack Harkness mortal. Throughout the series, former agents of the now defunct Torchwood Institute Captain Jack and Gwen Cooper allied themselves with CIA agents Rex Matheson and Esther Drummond to put the world back to normal. Discovering that the Miracle was the work of the mysterious organisation known as The Three Families, Torchwood reversed the Miracle with the help of Jack's mortal blood - and in the process made Rex immortal! Don't ask. Just go with it. And that's how it ends. With the Three Families still at large and ready for a 'Plan B' and a second member of the Torchwood team now immortal. As Davies is currently working on upcoming British drama series Cucumber and Banana, it looks likely that either Torchwood will be rested for a number of years or it is done for good, meaning we will never get the answer to what happened next. Unless a miracle occurs, of course.