Doctor Who: The Waters of Mars

The Doctor lands at the first human base on Mars in 2059 knowing that everyone there will die that day, because this death is a fixed point in history and cannot be altered. Then something waterborne appears. Directed by Graeme Harper, this special is regarded as among the darkest things the series has done, since the real event is not the infection but the Doctor deciding to break his own rule and what he becomes in the act. David Tennant makes him nearly unrecognisable by the end. The infection design and the water effects are impressive at television scale. It is one of the steps leading toward the close of the Tennant era. Who it is for: Doctor Who viewers and anyone who likes the darker science fiction episodes. Who it is not for: newcomers, since the weight of the ending comes from the past.