With the TARDIS working perfectly, the Doctor and Peri decide to take a holiday. But where? A long-forgotten piece of equipment in the TARDIS storage locker sends them to the peaceful and idyllic continent of Tranquela - home of the Doctor’s old friend Ravlos.

But the land where they emerge is far from peaceful. A hate ray is regularly sweeping Tranquela, turning its inhabitants into savage beasts, and there is only one place it can originate - the planet’s other continent, home of Tranquela’s old enemies, the Amelierans.

Or is that the only place? Because somewhere far above the planet events are watched by the slimy super-salesman, Mordant, who has his own unscrupulous plans.