When Noah brought the animals on his ark they came two by two. This fact makes for a fun bit of singing and wordplay for children first learning the story, but what’s missing is the why. The story isn’t told to children to explain animal husbandry, though, it’s told to extoll the virtues of faith, that listening to and obeying god is the only path to salvation. The image of the animals pairing off and boarding the ark along with Noah and his family also evokes another theme that runs deeper than faith: survival.

With or without Noah, the flood story persists around the world and across religious and cultural traditions. Aboard the TARDIS it transcends time and space. When the TARDIS materializes in a lush forest the Doctor (William Hartnell), Steven (Peter Purves) and their new companion Dodo (Jackie Lane) are sure they’ve landed on Earth. Despite the presence of lizards, birds, elephants and even people, they learn they’re actually aboard a spaceship, traveling along with refugees from a dying Earth, ten million years from the present.

The majority of people aboard the ship have been miniaturized and placed in stasis for their 700 year journey to the planet Refusis. Those remaining are called the Guardians, and they’re assisted in their duties by Monoids, refugees from another world.

Doctor Who: The Ark makes great use of the time travel conceit, moving the characters through the entire arc of the refugee’s journey to their new home. The story is split into halves, the first of which centers on the specter of disease, something the Guardians have eliminated over the centuries. It comes via Dodo, whose minor case of the sniffles turns deadly and quickly spreads throughout the ship. This gives Steven pause, and he utters a horrifying line: “Has this happened before?” Traveling to other eras and other planets, the Doctor and his companions could spread disease anywhere, wreaking havoc across the universe, an idea that could spawn a whole series of stories.

This idea of the Doctor’s legacy of disease is forgotten when a cure is found and order is restored, but for the Guardians traveling to Refusis, the legacy of their actions lingers long into the future. After the TARDIS leaves the ship it materializes again in the exact same spot as before, only seven hundred years later. The planet Refusis is in sight and the Monoids have taken control of the ship.

The second half of the story overshadows the first both in scale and excitement. The Doctor and his friends find a complete reversal of the world they’d only just left. It’s a wonderful bit of narrative sleight of hand that proves why the show has endured. Time travel doesn’t have to be about killing the dictator or righting some historical wrong. It allows us to peek ahead to see what comes next.

Doctor Who: The Ark marks the Monoids only appearance on the series. As goofy-looking villains go these guys are formidable. They look like stalks of broccoli wearing Beatle wigs and, when they gain the ability to speak, their voices are Dalek-lite. The transformation from servants to masters and their single, unblinking eyes give them enough depth and menace to make them convincing.

Among the brief but satisfying bonus features is the featurette “One Hit Wonder” which explores the Monoids’ status among other single appearance aliens, and the strange appeal of their ridiculous and scary look. “Riverside Story” details the making of the story and gives viewers a tour of the sound stage where it was filmed, and “All’s Wells” marks Doctor Who’s debt to the works of H.G. Wells.

Doctor Who: The Ark is a story of survival and endurance, something the creators of Doctor Who and its fans know a little about. There are bad stories, goofy aliens and lousy special effects littered throughout the series’ history, but stories like this help us keep the faith.