A group of conspiracy buffs have hired the PCs to go to several different worlds to investigate the events at
Roswell in June of 1947. They're well aware that all the worlds are different or are potentially different. So a few damp squibs won't be held against anyone.
Problem, Roswell was conducting real research involving military secrets. Just because their aren't any UFOs doesn't mean the PCs can't get arrested or shot.
Further problem, in some worlds their could be aliens. Then what?