Episode 1, originally transmitted on ITV, 9 January 1984

Matthew Gore is a perfectly ordinary schoolboy, today celebrating his 12th birthday with his family on a trip to the London Planetarium and Madame Tussauds.

One ordinary school day, Matthew is struggling to pay attention in a maths lesson on factors. He is an average student, not good or bad, but indifferent. The teacher sets a few factors problems for the class, but as they set to their work, a strange blue light enters a window and hovers over the heads of various pupils, before seemingly disappearing into Matthew's head. Within moments, Matthew is speeding through the questions and the teacher is astonished to find that such a middling pupil has answered all the questions correctly so quickly.

Back at home, Matthew asks his mother a curious question: why there are two sexes? Wouldn't one be more efficient? Later, when Matthew is doing some homework, his mother notices he seems to be talking to himself. Likewise, dad overhears Matthew sitting in the garden taking to himself, asking questions about the calendar and the rotation of the planets. Matthew's parents privately discuss this behaviour - perhaps he has an imaginary friend like his sister, Polly.

At the weekend, the family visit a farm and Matthew asks another curious question of his dad - why, if the cows are intelligent enough to know when it is time to go into the milking shed, can't they work out how to leave the field when it is obvious when the herdsman will leave the gate open? His father has no answer.

Over at his friend's house, Matthew almost absent-mindedly completes Colin's impossibly difficult Rubik's Cube puzzle. He seems almost ashamed to have done so. He asks Colin if he sometimes hears a voice talking to him in his head. Colin warns that Matthew will end up in a 'loony bin' if he carries on talking like that.

Matthew is taken ill with a fever and sent to bed. Sweating and seemingly delirious, he calls out, asking for 'Chocky' to go away. He pleads with his mother to make Chocky go away. Gently his mother suggests to 'Chocky' that Matthew needs his rest. The boy seems to relax and falls asleep. Matthew's parents are left wondering who or what is Chocky?

In his bedroom, a blue light seems to dance over Matthew's head as he sleeps.