Devour

"Devour" is the sixth episode in the ninth season of Doctor Who, set on 24th century Earth where a mysterious virus is eating away at human flesh.

Synopsis
"Limbs and what not are dropping off like that, its leprosy gone wild" - Doctor Praytira

The Doctor and Billy arrive on Earth 2555 A.D, where a mysterious alien virus is eating away people’s flesh. The Doctor seems puzzled, but soon the virus grows to horrific heights and thousands begin to die. Discovering the source of the virus, a dying Cystaron K’heltan, who is spreading his dying spores throughout the air and infecting humanity. The Doctor first believes K’heltan’s lies, but soon discovers he is using the virus to sustain his life.