Full Fathom Five (2 parts)
Off the coast of NW Scotland an oil rig is being plagued by mysterious events. Machinery failing, strange health issues and ultimately a worker called Mason goes missing.
UNIT is dispatched to the rig to find out what is going on. Accompanied by technical expert Lt Sanders (Colin Baker) they start a full investigation into a new sector which has recently revealed a potential new seam. Meanwhile Jock is amazed to find and old friend there. Bob (Gregor Fisher) has been working on the rig for 3 years and is able to tell Jock that something strange has been going on. A senior manager called Carlisle (Frank Finlay) has been brought in by the company to oversee a new project. Jock asks what the project is. Bob doesn't know but he does say its something to do with the new seam...
Sanders and Fisher are examining the machinery and are puzzled to see that there is some kind of strange skin-like substance on the cabling.
Reynolds questions Carlisle about why he has been transferred to the rig. Carlisle says he cant say without permission from the company's HQ in Aberdeen and its highly unlikely that he will be given permission. Carlisle goes on the say that the company has attached a high level of importance to the new seam and that he cannot and will not jeopardise it.
Jones meanwhile has been examining the substance on the cabling and tells Sanders and Fisher that is a form of skin...non-human
Later on Bob is looking for Jock. He walks down a corridor. The lights go off and there is a bloodcurdling scream. As the lights go back on UNIT race to the corridor and find Bob dead, covered in oil and the same substance
In a makeshift morgue Jones states that Bob was struck over the head causing brain damage. Jock is devastated and goes to find Carlisle. Reynolds, Fisher and Sanders have to get between Jock and Carlisle to prevent an incident. Reynolds order Wallace out. Turning to Carlisle Reynolds demands the truth.
Carlisle explains that the oil found in the new seam was synthetic. It could be replicated leading to a new infinite source of power. The company send him to oversee the replication process. Mason was send to collect a new sample and he had vanished.
UNIT along with Carlisle enter the area where Mason vanished. Going deeper into the bowels of the rig they encounter a pool of the synthetic oil. A form rises from the pool. It is Mason. The voice however isn't human.
It goes on to say that it is a lifeform that was Earth long before humans and can invade human tissue. They lived in the deep of the oceans and seas in peace before the humans started digging. One of them was killed by the drilling. In revenge they killed Bob.
Carlisle apologises for the death. Reynolds asks if there's anything they can do. The lifeform simply asks "leave us be"
The company orders that the seam be left alone.
As UNIT flies away. One question remains. What other lifeforms exist on Earth?....