A special force of interdimensional operatives protect the universe from evil forces trying to gain a foothold by disrupting the timeline. The strange energy beings are assigned to cases, when and where needed, and materialise on Earth as humans, each with specialist abilities to ascertain and then solve the problems. The mysteries encountered by Sapphire, Steel and their colleagues include people trapped in photographs, ghosts lost in time, and a dinner party of guests who are all long-dead.