A shapeshifting alien is in pain, currently only a gray blob focused solely on finding the greatest mathematical mind in the solar system to open up a special vault on Mars that only responds to prime numbers so the monster inside can have the ultimate meal. A human is walking the corridor in the engine room of the spaceship that the shapeshifter had stowed away on. The shapeshifter tries to take over the man's body, but he fights it off and in the ensuing chaos he steals a chunk of its dissolving flesh as it escapes out of a window into space. Latching onto the side of the ship, the shapeshifter rides it down onto the planet and takes over a stranger's body. Every time it does so, it steals their memories. But only after it kills them.

Going into an stock brokerage, the shapeshifter finds who it is looking for: the head of the company who is really smart. In his office is a bit of metal from Mars, where he has just returned from. The shapeshifter, now in the form of this man named Jim, tries to convince him to come back and open up the hidden vault where an extra-solar beast the Martians were deathly afraid of was locked away. Jim refuses to help, and kicks the shapeshifter out so he can start another meeting. The shapeshifter follows the man who came after him for the meeting, a rival of Jim's from another company, and takes over his shape before gruesomely murdering him. It set about finding and killing off all the major leaders of every stock brokerage in the city. Upon doing so, it would sell all of the stocks connected to companies that Jim's invested in, bankrupting him. Jim had no choice but to follow the shapeshifter into space to reclaim his fortune with tons of old art and furniture from Mars.

Jim did exactly this, joining the shapeshifter, now disguised as the captain of a freighter, into space heading for Mars. But Jim, suspecting something, called back to the planet during their flight and saw the real pilot warning him about the shapeshifter. Jim shoots the shapeshifter, trying to drive it into a vat of the Martian metal that it can't escape from, but the Controller who created the shapeshifter takes over its body and talks to Jim through it. The Controller explains that they are a race of beings from a different dimension where math is different. They need the best mathematician to help open the vault where their colleague was placed by the Martians nearly 100 million years ago (which is only a year or two in their time). Jim believes this and chooses to help free the beast.

Once there, Jim figures out the time lock and the beast is about to be freed. Jim realizes he was duped after the Controller tells him such through the shapeshifter. With great effort, the shapeshifter destroys the lock instead of opening it, killing the beast inside. When Jim asks why, the shapeshifter says with its dying breath that it hated its masters for bringing pain to it, and really loved being human because it liked having an identity. Jim heads back to Earth a rich man, and his wife who left him when he lost all of his money comes back.