From Amazon.co.uk:

Luck is on the side of most during the incident at the Four Aces Casino and Hotel, when the simmering tension between two rival biker gangs suddenly boils over into all-out violence -- miraculously, there are only two fatalities despite the hundreds of rounds fired on the casino floor. Called to an out-of-control crime scene located outside Las Vegas in the legendary town of Boot Hill, forensic investigators Gil Grissom, Catherine Willows, Nick Stokes and Sara Sidle quickly discover that the casino shootout victims were no innocent bystanders: one was the powerful leader of the Predator gang, and the other a luckless card dealer who may have borne witness to an elaborately staged execution. Meanwhile, back in the glitter of Sin City, CSIs Warrick Brown and Greg Sanders have their own hands full, as the dark side of this desert metropolis is about to wreak havoc on the two investigators via a seemingly endless series of crimes...