Disillusioned with the treatment of the Earth at the hands of modern society, several influential men get together and form Operation Golden Age, devoted to returning the Earth to the halcyon days of old when pollution was nonexistent and the planet was respected. But their intention was not to influence current government policies; their intention was to turn back time to an earlier period of Earth's history. They persuaded others to join them with the promises of sending them on a six-month journey in a state-of-the-art spaceship to New Earth, an undefiled planet at a stage of development similar to early Earth, populated by a simple people who they could guide toward environmental respect. They were unaware that the spaceship was fake, merely a room within the Operation Golden Age complex, and that the group was planning to reverse time on Earth, erasing the subsequent timeline and creating a new one with their own influence. A protective field around the complex would protect the people within it from being affected by the temporal reversal, leaving them safe to step outside and live on their new Earth.
In order to test their time equipment, and give them the time they needed to finish preparing for their journey, the group used their equipment to snatch dinosaurs from Earth's past (and occasionally a rogue human from different periods of Earth's history) and deposit them in central London. With dinosaurs appearing out of thin air, rampaging around, and then vanishing without a trace, all eight million people in central London were evacuated. Soon the city was populated only by roving tyrannosaurus rex, triceratops, stegosaurus, brontosaurus and pterodactyls.
When the Doctor was called in, he discovered that the dinosaurs were being snatched away from London in a time eddy, which made time reverse for a few seconds and caused the dinosaurs to return to their own time. The temporal displacement caused a localized distortion in time, which meant that the people in the immediate vicinity had no recollection of the time eddy or what happened to the dinosaur. When Sarah tracked down the headquarters of Operation Golden Age and passed its location on to UNIT, the Doctor was able to reverse the polarity of their time equipment. When they tried to undo his damage, the equipment disappeared and the leaders of the group were sent back into Earth's distant past.
