When young Matthew starts talking to himself, and introduces his invisible friend Chocky to the family, his parents decide it's just a phase he is going through.

But when Matthew starts explaining binary maths and anti-gravity propulsion, they begin to worry.

Is Chocky really just the product of an over-inactive imagination, or something more?

Based on a novel by John Wyndham, this full-cast radio drama was first broadcast on BBC Radio 4 in 1998.