The Goal: Locate a viable source of blood for the dying race of Davannans, whose bodies are ravaged by radiation bombardment from ongoing nuclear war.
The Plan: Several phases outlined in detail, but it boils down to:
1. Dispatch a representative from Davanna to Earth. Disguise him as a rich weirdo called Paul Johnson, and cover his milky white eyes with sunglasses 24/7. Employ juvenile delinquent manservant for menial tasks like operation of Earth vehicles and guarding the corpse-burning oven.
2. Force Earth doctors to provide blood transfusions without explaining why. Employ live-in nurse for daily home transfusions.
2a. If Earthling blood proves a compatible replacement, enslave the planet and steal all the human blood. Skip to #3.
2b. If Mr. Johnson dies, destroy the planet.
3. When the blood is used up, destroy the planet.
Supplementary Tasks: Procure extra blood samples from winos and vacuum cleaner salesman Dick Miller by means of a blood-sucking briefcase. Probably these are for study, but store them in the fridge. Also, accidentally smush a hapless Asian-American fellow to death in the interstellar matter transporter while attempting to mail him home as a "sub-human specimen."
Contingency Plan: Mind-control, telepathic linking ability and eye-contact-activated ocular death ray should cover most emergency situations. Should worst come to worst, dispatch flying bat-octopus-umbrella minion that can eat peoples' heads. [NOTE: When not in use, Vampire Umbrella Bat should be wadded up to look like a celery and stored in cellophane.]
Is the Plan Sound?: The blood procuring scam is okay for a last ditch effort. "Species facing extinction" angle adds sympathy, but that is mooted by overt racism and intent to destroy the planet without motivation.
This is the way the world ends.