The Ark in Space

The Doctor and his two travelling companions, Sarah Jane Smith and Harry Sullivan, arrive on an apparently deserted space station orbiting Earth in the far future. They discover that the deactivated Space Station Nerva, known as The Ark, contains the last survivors of the human race in suspended animation. Earth having been evacuated thousands of years earlier when solar flares threatened to destroy all life.

On The Ark they discover that the sleeping humans have not reawakened when they should have, because of a fault in the station’s power supply. After getting past the onboard security systems The Doctor and Harry realise that Sarah, after becoming trapped in a sealed room and nearly suffocated due to a damaged air supply, has trigged the automated hibernation unit and has inadvertently been placed in suspended animation with the other sleeping humans.

What they do not realise, at first, is that The Ark has been invaded by a Wirrn Queen, a large insect like creature, who has other plans for the sleeping humans. Before the TARDIS arrived the Wirrn Queen had already taken the body of Technician Dune, and with his knowledge of the space station, had laid her eggs close to the solar stacks - The Ark's power source - intending to use the remaining sleeping humans as food stock for her young. Then, with her task completed, the Queen had hidden herself away in a storage locker and died.

The Doctor

On arriving at the hibernation area The Doctor and Harry manage to locate Sarah in suspension in one of the cryogenic pallets. Harry, while searching in some cupboards for a resuscitation unit with which to revive Sarah, discovers the dead Queen. They then realise that The Doctor's reactivation of the space station's systems has caused the revival of the humans to start. The first human to be revived is Vira who agrees to help revive Sarah. The Ark's leader, nicknamed Noah, is also revived but when he goes to examine the solar stacks he becomes infected by one of the emerging larvae.

The Doctor realises that Noah, who starts to act strangely, is turning into a Wirrn. Noah though manages to fight off some of the alien influence and orders Vira, via the communications system, to expedite the revivification and get everyone off the station before the Wirrn absorb them and then take over the Earth.

The Doctor and Harry

Realising the danger they are all in The Doctor and his friends gain the trust of the other humans and, while Harry and Sarah start to revive the rest of the technical crew, The Doctor and Vira go off to find Noah. They soon discover him and Vira is shocked to discover that a growth has taken over most of the left side of his body. With Noah no longer fit to be the leader Vira takes command. However, Vira wants to carry out Noah's last orders and continue the revivification, until The Doctor points out that it will take too long, as the Wirrn will have matured from their larval stage into adults before then. He argues that to defeat the Wirrn they must be destroyed while they are in their dormant pupae stage.

However, after fending off an initial attack and knowing that the Wirrn have at last become dormant, The Doctor goes to the power room, where he finds the Wirrn pupae. As he tries to reactivate the solar stack, Noah - by this time fully transformed into a Wirrn - attacks him.

Fortunately, Vira and Sarah have followed The Doctor and so are able to rescue him. As they back out of the room, Noah tells Vira to leave the station in the transport ship, or else the Wirrn will hunt them down when they emerge. Noah then explains that a thousand years ago, the Wirrn were driven from their home, Andromeda, by human space settlers. Since then, they have drifted through space, looking for a new world, and have now claimed The Ark for their own. While the Wirrn can live in space, their breeding colonies are terrestrial, and they need humans as hosts. They intend to absorb all human knowledge, achieving revenge for the loss of their original home and becoming an advanced technological species within a single generation.

Sarah on the Transmat Table

After the failed attempt to destroy the Wirrn The Doctor suggests that they somehow electrify the cryogenic chamber to stop the Wirrn from feeding on the sleeping humans. But as the Wirrn control the solar stack they have no means to maintain the electricity. Sarah suggests using the transport ship, which must have its own power generators. After running a cable through conduits, to prevent the Wirrn cutting it they are able to electrify the walls of hibernation area so driving the Wirrn back.

Realising what The Doctor and the humans have done the Wirrn Swarm Leader, offers the others safe passage from The Ark if they leave remaining un-revived humans for the Wirrn. If they do not, the Wirrn will shut down the oxygen pumps. The Doctor tries to appeal to what is left of the human in Noah with reminders of what Earth is like, asking him to lead the swarm into space where they belong, but Noah claims he has no memory of Earth. Meanwhile, the Wirrn try to board the transport ship in an attempt to cut off the power supply.

There is nothing The Doctor can do to stop them and so orders Vira to initiate automatic take off and evacuate the space ship. With all the Wirrn inside the transport ship heads off into space. Suddenly without warning the transport ship explodes – it seems that in a final act of humanity, Noah deliberately neglects to set the shuttle's stabilisers so destroying himself and his fellow Wirrn.

With the threat over The Doctor agrees to help Vira and offers to pop down to Earth using The Ark's transmat system to ensure that the diode receptor beacons are correctly tuned in order to receive the returning humans. Sarah and Harry elect to accompany him and so all three depart leaving the TARDIS still aboard The Ark.