Fifteen hundred years in the future, a young couple occupy an invisible time capsule and attempt to live in the twentieth century as part of an experiment.
A couple from 1500 years in the future occupy an invisible time capsule atop a modern-day block of flats as part of an experiment. Time is resentful that, in the couple’s home time-zone, man is the only animal not extinct. It begins to menace the couple and their baby with animal-derived products. The baby is made to age into an adult and given the power to age or regress material objects. Sapphire and Steel are joined by Silver and confront this changeling. Silver is sent into the future and Steel destroys the changeling reverting it back into a baby and returning Silver. The agents track down the source of the disturbance, an amalgamation of various types of organic matter, and Steel terminates the experiment.