This one puts the action on the International Space Station, whose six-person crew have just discovered a single-cell organism, the very first evidence of life outside of Earth, within one of the soil samples they've taken from Mars.
Powers that be at home want them to do some testing on Calvin, as they've dubbed it, before giving the “all clear' to bring down to a terrestrial lab. Study they do, as Calvin begins to flourish in his new environment, grown far beyond its single-cell existence. However, like the humans on board, it needs oxygen and food to survive, and to eliminate all potential threats, which means that Calvin takes a feed-and-fight approach to any other creatures that might encroach on its new home on board the space station. Meanwhile, the astronauts and scientists do everything in their power to quarantine Calvin, especially in making sure that the deadly entity does not have a chance to reach Earth.