Adventure in the 5th Dimension!

Mostly written in Atari BASIC (with a hint of 6502 assembly), this game was Brian Moriarty's first text adventure. Its player controls a private investigator on the trail of extra-terrestrial burglars who have stolen the Declaration of Independence! There are clues to be found in the "maze of streets" representing Washington D.C. and, of course, there is the upper dimension promised in its title to be traversed with the game's text parser interface.