In what story there is, amiable Hoyt Axton comes across a mysterious creature in Chinatown and takes it home as a Christmas present for his likable teenage son, Zach Galligan. With the gift, he passes along a warning from the inscrutable Chinese that the creature must never get wet, be allowed into the sunshine or fed after midnight.
For a while, all is extremely precious as the little furry thing goes through an array of facial expressions and heart-warming attitudes.
Without giving away too much, suffice to say the creature spawns a townful of evil, snarling, drooling, maniacal killer-creatures who are bound to cause a lot of woe before their predictable downfall.
The humans are little more than dress-extras for the mechanics.