If you play a version of the original MIT Zork (often called "Dungeon"), you'll find it isn't exactly the three games put together. There really isn't much plot

If you play a version of the original MIT Zork (often called "Dungeon"), you'll find it isn't exactly the three games put together. There really isn't much plot in the original -- like Zork I it is just basically a treasure hunt (as was the Colossal Cave Adventure which inspired it). There are additional puzzles and plots in Zork II and III that have no basis in the original.