The Slaver Weapon: A great ep

In this episode, written by veteran sci-fi author Larry Niven, Spock, Sulu, and Uhura are returning to the Enterprise in a shuttle, carrying what appears to be a weapon from an ancient dead race, called the Slavers, when they are captured by the Kzinti, a race of cat-like people who are looking for an edge to fight the Federation. The cool thing about this weapon is that it has 7 or 8 settings which change the appearance of the weapon, but it doesn't seem to function on any of them. Eventually the weapon's purpose and its awesome power is revealed and the threat to the Federation could not be greater should the Kzinti be able to harness it for a planned war. Great mystery, great suspense. One of the best episodes and very spooky too.