Now available from the BBC is the two-disc Doctor Who - The Ark in Space Special Edition. The second serial in the 12th season, these four half-hour episodes have been called the best of the classic Doctor Who by both Russell T. Davies and Steven Moffat, both driving forces in the latest reincarnation of the show.
Originally airing in January and February of 1975, The Ark in Space, opens with the TARDIS landing on a seemingly deserted, aged space station; it's a creepy place. It isn't long before the Doctor (Tom Baker) and his companions Sarah Jane Smith (Elisabeth Sladen) and Harry Sullivan (Ian Marter) discover that the place isn't nearly as empty as they first think. There is an entire population of humans slumbering peacefully within, frozen in cryonic suspension, waiting to awaken and find a new home to settle in.
But the ark should have already reached its destination, and the people should already be living their new lives. Instead, a dangerous alien parasite known as the Wirrn have taken over the craft. When a few crewmen are woken by the Doctor and his friends, the insect-like creatures take over the captain of the ark, called Noah (Kenton Moore), and the humans must engage in a deadly face-off with these things.
The Ark in Space is credited as being the first to show a darker side of Doctor Who, bringing a horror element to the series that continues to this day in "Blink" and other episodes of the modern version, most notably the ones featuring the angels. Doctor Who wanted to expand its appeal more towards an adult audience at the time, and this is how they chose to do it. They didn't go too far, even cutting out some footage deemed "too scary." But this is a turn away from the show's lighter, fluffier stories.
Part of why this serial is different from that which came before is the level of danger threatened by the enemy; there are casualties and heart-wrenching deaths. People cannot all be saved, and the ending is only happy for some, mixing tragedy into the finale. For those who have seen many episodes of Doctor Who, this may not seem all that novel or different a concept in 2013. But for the time period it aired, it represented something very fresh. And the experiment worked, buoyed by fantastic performances and a gripping script, garnering high ratings and forever changing the series.