In response to The Brigadier's summons The Doctor, Sarah Jane Smith and Harry Sullivan return to Earth. On arriving, in the TARDIS, they discover that UNIT are investigating a series of mysterious attacks on North Sea oil rigs off the Scottish coast and has set up a temporary HQ in the Scottish village of Tullock.
The Doctor, who is somewhat dismissive of the urgency, reluctantly agrees to help The Brigadier. In the meantime, Harry finds a body washed up on the beach, but when he tries to help he is shot by the Caber, a highland gamekeeper employed by the Duke of Forgill.
Harry is taken to the sick bay, of the Hibernian Oil Company, to recover from a head wound he sustained when he was shot. However, when Sarah telephones The Doctor from the infirmary, to notify him of Harry’s health, their conversation is interrupted when Sarah is attacked by a hideous orange humanoid monster and knocked unconscious. When she comes to she finds herself locked in a de-compression chamber used by deep-sea divers.
|Sarah Jane Smith
Rescue comes from The Doctor, who has rushed over to the infirmary. However, as The Doctor tends to Sarah they both become trapped in the de-compression chamber and to Sarah’s alarm the air pressure in the chamber starts to decrease as the air is pumped out and Sarah starts to suffocate. The Doctor though is able to save her by putting her in a trance so that she no longer requires too breathe until they are eventually discovered.
To investigate things further The Doctor decides to go out on to the moor. However he is unaware that a homing device has been slipped into one of his pockets. This homing device attracts the attention of a huge cyborg creature called the Skarasen. As The Doctor races across the moors to try to escape from the pursuing Skarasen he eventually trips and falls to the ground. These events though are being watched by an alien creature who gives the order for the Skarasen to kill him. The Doctor, desperate to find something to defend himself from the Skarasen that is bearing down on him, luckily discovers the homing device which the Skarasen follows when The Doctor throws it away from himself.
This attack makes The Doctor realise that the oil rigs, that were destroyed by what the crews have described as something huge and monstrous, must have been attacked by the same creature that attacked him - the Skarasen. He also deduces that the attacks are being controlled from Loch Ness.
However, while all this has been happening Harry has been abducted and duplicated by one of the orange humanoid creatures. The Doctor realises that the Duke of Forgill himself is involved, and in Forgill Castle Sarah discovers an entrance to an underwater spacecraft.
This spacecraft, which is lying at the bottom of Loch Ness, belongs to the Zygons, who centuries ago arrived on Earth, and with their ship crippled, awaited rescue. On becoming aware that their home planet has since been destroyed, by solar flares, the Zygons plan to take over the Earth as a substitute for their own planet. They are therefore using their shape-shifting abilities to take on the identities of locals whose inert bodies are held aboard their ship.
The Doctor manages to infiltrate the Zygon’s spacecraft and release all the prisoners. He also causes the spacecraft, which has now emerged from the Loch, to self-destruct. However, the Zygon’s leader, Broton, survives. He has taken on the form of the Duke of Forgill to infiltrate a World Energy Conference in London which he plans to destroy.
On realising what Broton is intending to do The Doctor, with Sarah and The Brigadier, races to London. As they arrive Broton places another homing device in the basement of Stanbridge House, where the conference is being held, so as to attract the Skarasen which is now approaching up the Thames.
On discovering Broton in the basement he is shot by UNIT troops. They then desperately search for the homing device. On its eventual discovery The Doctor throws it to the Skarasen, which devours the device. The Skarasen, now without any controlling influence, makes its way back to the only home it knows, Loch Ness, there to be occasionally mistaken for the fabled Loch Ness Monster.
With the crisis over, and on returning to Scotland, The Doctor and Sarah decide to travel back to London in the TARDIS, but Harry, feeling that his time with The Doctor has all got a little too much for him, elects for the safer and more reliable method - by taking the train.