The peace and quiet of a remote homestead in the 1880s American West is shattered by the arrival of two shadowy outriders searching for 'the healer'. When the farmer refuses to help them, they raze the house to the ground using guns that shoot bolts of energy instead of bullets.

In the town of Redwater, the Doctor and Martha learn of a snake-oil salesman who's patent medicines actually cure his patients. But when they investigate, the truth is stranger, and far more dangerous.