The Doctor has regenerated, to the mild consternation of his UNIT colleagues and companion Sarah Jane Smith. This new Doctor is less wedded to Earth and his work with UNIT, and is eager to resume his adventures in time and space. But a demonstration of the TARDIS to UNIT surgeon Harry Sullivan sets in motion a chain of events that'll see the Doctor and his companions marooned on different planets and in times without the TARDIS to rely on. It's going to be a long trip home.
