A mother and father disappear from their remote, coastal home whilst reading nursery rhymes to their daughter. Their fourteen-year old son Rob rings for the police, but it is time-agents Sapphire and Steel who come to the rescue.
In a large, remote, coastal house, a mother and father read rhymes to their daughter. Downstairs, fourteen-year-old Rob is doing his homework. One by one the clocks stop and his parents vanish. Rob phones the local policeman and, seconds later, Sapphire and Steel arrive. They are menaced by Roundhead soldiers and images of plague victims. Sapphire becomes trapped in a painting and Steel reduces his body temperature to absolute zero to release her. Eventually, together with another elemental called Lead, they lure the enemy into the cellar. Here the force is crushed out of the foundations of the house by Lead. Sapphire and Steel disappear and the parents return as though they had never been gone.