Haemovores are at the end of a possible evolutionary path for the human race: they are vampiric mutants whose origins lie in the pollutants with which, in the far future, man poisons the Earth. If man cleans up the Earth and stops pouring chemicals and sewage into its seas and oceans, the Haemovores may never have been: their appearance will have been nothing more than a temporal paradox.

Known as the Ancient One, the first of the Haemovores has by far the greatest powers. It is to the lesser Haemovores what Dracula is to the vampires he creates: it guides them mentally and can destroy them by exerting its will through the telepathic link that binds them. The Ancient One and lesser Haemovores alike can all create new Haemovores by draining the blood from their victims: anyone killed by a Haemovore in turn becomes one.

At first, a newly created Haemovore resembles the person it once was. Its skin, however, is now a deathly white; its lips, a full red; and its fingernails, long talons. Although it still has the power of speech, its voice has become harsh and sibilant. In time, as the chemical mutation passed on by its creator takes hold, a new Haemovore loses the power of speech and communicates through telepathy. Its skin, too, changes: it puffs up and turns pale blue, becoming encrusted with white, barnacle-like growths. A millennium or two of mutation produces the final form: a broadly built, 2.2 metre tall creature of like power to the Ancient One.

The creatures live in small communities in the depths of the oceans, or in wrecks and caves on the seabed. Each community is led by the oldest present Haemovore, the one with the greatest powers. Only their craving for human blood -- a scarce resource in their future Earth -- brings them from the oceans. Much of their power for rational thought, however, has gone; they have become creatures of instinct.

Fenric, an evil intelligence banished for centuries into the shadow dimensions by the Doctor's trickery, brought the Ancient One back through time to twentieth century Earth as part of a trap to catch the Doctor. Although the Ancient One perished, and Fenric's physical form was again destroyed, the Haemovores may yet again rise from the depths.