From the introduction:
This is an adventure for Traveller, but one with a difference.
Instead of playing in the far future, the players will be thrown
into the Wild West. The action takes place in and around the
frontier town of Bent River, though the players will discover
heavy shades of science fiction soon make themselves felt.
Referees should take pains at not telling the players the title
of this adventure, as the presence of aliens in the Wild West
should be sprung upon them. Instead, tell them it is called
something like The Last Ride of McCreedy, or The Rise of the
Sioux, or anything that does not have the words xenomorph or
alien in it! The adventure starts off like a normal Wild West tale,
but things can get weird very quickly!