A savage storm; the crew of a sinking vessel is forced to take shelter aboard a mysterious ship, which they find to be empty except for the sole survivor of a sinister, ethereal force that has killed all others.
Sounds like the making of ghost story. Here, however, the writers have steered away from the fanciful notions of the supernatural, turning to the thoroughly believable concept of aliens. Yesterday's spectre is today's space-creature.
The story starts when a massive, blue, crackling cloud of energy envelops the MIR space station, overloading the circuits and killing the crew. At the time, the station was communicating with a Russian science ship in the South Pacific, and so the entity follows the transmission down and invades the ship's electronic systems.
Days later, the Russian ship is found in the eye of a typhoon by the ocean-going tug Sea Star. The crew, headed by Captain Everton (Sutherland), navigator "Kip" Foster, and engineer Steve Baker (Baldwin); claim the apparently abandoned Russian ship as salvage. They find Nadia, the only surviving crew member, who tells them of the alien.
Despite their initial doubts, when the ship's computer declares that the humans on board are a biological contaminant that must be eradicated, they have little choice but to accept Nadia's story, as the entity begins to hunt them down.
A thriller movie, this is, as I said, today's version of the ghost story. It also bears some suspicious similarities to Alien, but fans of the genre should consider that a plus.

Long before Jurassic Park, Michael Crichton had this book made into a movie. Crichton likes to play with the implications of science for society. The Andromeda Strain looks at biological warfare.
A satellite crashes near a remote desert town, and all the inhabitants (save a drunk and a baby) die soon thereafter. A team of scientists previously involved in work on the satellite are assembled at a secret base nearby, where they must race against time to find out what happened and how the problem can be defused. Concentrating their minds is a nuclear bomb that will go off if the base becomes contaminated. You won't be surprised to find out that the bomb plays a key role in the movie's third act.
The movie eschews romance and special effects (just as well, since it was made in 1971 and they'd look laughable anyway) in favour of a quasi-documentary look and plenty of scientific explanatory dialogue. It's interesting that later movies of Crichton's work usually to deliver the science in a brief expository scene before getting on with other things; this makes no such concession.
Incidentally, the director, Robert Wise, also directed a number of classics, including The Day the Earth Stood Still, West Side Story, The Sound of Music, and (rather more mediocre) Star Trek: the Motion Picture. In some ways, Andromeda Strain feels like the latter: slow-moving (particularly in the middle) and with a serious purpose.