They arrive during a festival, and meet Professor Stream, his assistant Jane, and his chauffeur whom the Doctor nicknames Steel Specs.

As they look for Foxwell, Peri encounters the young Simon, who claims to have seen a sand monster, while the Doctor's curiosity is piqued by a glowing object being sold in a white elephant sale.

With Foxwell's equipment, the Doctor determines that the glowing object is a scale from a Tractator, an alien species that resemble the sand creature Simon saw and which have the ability to control gravity.

They race to stop the initiation of the engine, but arrive too late, and the Doctor, Peri, Simon, and Foxwell are trapped in a collapsing bubble of space.

There they come across evidence that Stream has no credentials and never worked alongside Foxwell, and he has managed to seemingly insert his faked background to everyone's mind, including that of the Doctor.