Viva Las Vegas
A request for help summons Elvis and friends to the small frontier town of Las Vegas, a wretched hive of scum and villainy, where law-woman Billie ‘Doc’ Holliday is trying to bring the infamous Grissom Gang (siblings Gus, Gil, Nick, Greg, Catherine, and Sarah) to justice. Unfortunately they own the mayor and most of the gambling hells in the town, and the adventurers will soon find themselves seriously outnumbered if they try to meet force with more force.
As an additional complication some of the Grissom Gang’s thugs have been murdered, their bodies found with the letters “CSI” carved into their foreheads. Nobody is entirely sure what this means, though there are rumors of a "Cinco de Septiembre Independencia" movement in the town’s Hispanic population; there’s nothing obvious in the town records to explain why the fifth of September should be important, but it’s already late August, the thugs have begun to retaliate against anyone who looks Hispanic, and tempers are running high.
What’s needed is a cunning plan or two, preferably one that tackles the problem indirectly. For example, most of the gang’s wealth comes from gambling; if customers start winning they’ll soon be in trouble. This may be a good opportunity for a guest appearance by gambler Wild Bill Gates, possibly helping the adventurers to run an elaborate scam from his riverboat casino. Another possible target is the disused mine which the gang uses as its "bank vault"; of course this is protected by a variety of traps, ranging from primitive rock falls to high-tech sensors and laser-tripped mines, and looks disturbingly like the dungeon module of your choice...
This lets me use speakr2customrs' name for the CSI movement without having to explain what the date means, and I've added Gus Grissom to the list of gang members as suggested by robertprior. Later - added the "disused mine" on gonzo21's suggestion.