Sapphire & Steel - Season 1 Episode 1 Assignment I: Escape through a Crack in Time (1)

On an ordinary evening, a mother and father sing nursery rhymes to their daughter Helen before bed. Their teenage son Robert becomes alarmed when all the clocks in the house stop working. He hurries upstairs to find that his parents have vanished. Left alone with Helen and no neighbors nearby, Rob calls the police for help. But a pair of strange, time-traveling agents named Sapphire and Steel arrive instead and inform Rob that they are his only hope in getting his parents back.