Spain, Plannetta, and Castle are the outcasts of society. However a secret society called the Invisibles has uses for them. As long as they pass the initiation test.
They will be innoculated and a parasitic alien will bite them and take over their mind. If the crab like creature is attached to their back, they fail the test as they will be deformed.
Their purpose is to take over key figures in government, politics, finance and business. Eventually take world control by infecting key people.
Only Spain (Don Gordon) is a government agent sent in to infiltrate the Invisibles. Only he is suspected of being a spy very early on.
The Invisibles is a very creepy episode, atmospherically made. It is very much inspired by the Invasion of the Body Snatchers.
The crab like monster is eerie with its little legs being moved by a motor. The slow movement lets it down.
Gordon is very good as the agent who knows they are on to him and fears that he has no one to trust. At times the story is let down by some unnecessary melodrama. Spain is badly injured but manages to get so far even though he is in great pain.