Jeff Marx wants to study medicine and become a physician. However, his grades are far from enough to get him into an American medical school. But then he gets a chance to study medicine abroad in a small Latin American dictatorship governed by the dictator Ramon Madera who has a big interest in how the medical students behave.
On the planet Vortis, the Doctor and his companions aid the butterfly-like Menoptra in their battle against the parasitic Animus and its mind-controlled minions, the ant-like Zarbi.
The Doctor and his companions are pursued through time and space by the Daleks on the desert planet Aridius and beyond.
