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.