Old West Murder Mystery
Decorate part of your house to resemble a saloon with you as the owner. Set up bar stools and decorate the walls with vintage weapons, stable equipment and painted portraits in wooden or gold-tone frames. Throw checkered table cloths over metal or plastic tables and leave wooden tables bare. Set up a bar counter complete with a large square mirror framed on the sides with bottles of alcohol and soda. Hang a checkered curtain between the saloon area and the kitchen and close off undecorated parts of the house.
Cast friends as the sheriff, saloon girls and cowboys for the detective and suspects. Have the murder happen while the guests play cards and dine on appetizers by shooting a cap gun in an unseen location and having the victim fall into the main room. Require everyone to wear period dress and set up a table for the sheriff to display clue items. Play vintage piano music in the background.
Spooky Mystery
Style the party area to look like Dracula's castle or a haunted house. Cover the walls in black paper, or stone background paper, available at party stores. Set coffins against the walls, use lace spider web table cloths and hang fake spiders and bats from the ceiling. Play spooky sound effects in the background and set motion-activated booby traps around the house to frighten your investigating guests. Serve food with a strange twist, like black pasta or gravy with red food coloring in it.
Cast yourself as the manor's owner; you can be a vampire, witch, wizard, or mad scientist. Cast the detective as a Jekyll and Hyde personality that turns without warning and the suspects as angry ghosts, fortune tellers, and mental patients. Cast one or two "normal" people and have one of them be the murderer for a twist. You can frame a vampire with a barbecue fork as the murder weapon.
Tropical Resort Mystery
Plan this game in the summer. Set up outdoor games for your guests, a buffet with fresh fruits, punch and other tropical snacks. Decorate your home with tropical flowers, shells, bamboo screens and tiki torches, including plenty of torches outdoors so you can play at night to add to the mystery.
Cast yourself as the resort's owner or manager. The detective can be a modern detective in a slick suit, with the suspects as the bartender, the cook, a maid and several patrons. All of the patrons should be wealthy; they can be artists, business people or lawyers. "Poison" the victim during dinner for a dramatic death. In a twist, have the detective be the murderer.