The Sign of Diolyx is a Big Finish Productions audio drama based on the British science fiction television series The Tomorrow People.

From their secret laboratory deep beneath the streets of London, aided by their super-computer TIM, they watch and wait for others like themselves - and guard against threats to all mankind.

John and Paul travel to the Welsh village of Llan-Gwyliadwriaeth, but find that a psi dampening field is hampering their investigation and that young Alison Hardy has no intention of embracing her dormant powers.

Meanwhile, TIM discovers an energy signature connecting the village with a mysterious ship in hyperspace.

Against Tim's better judgement, Elena goes to investigate and finds herself trapped with a ravenous alien entity.