The story goes that when Jesus was crucified that his cross was put up between two thieves. One repented for his sins before the son of god, and the other jeered and taunted Christ instead.
Some time in the 15th Century an unknown sculptor of incredible genius created his masterpiece work "Christ and the Thieves", three works carved from olive wood that were so well done many people have thought that they were living people being crucified when the lights are low. Even more incredible are the signs and wonders associated with the statues. The Christ is said to occasionally bleed from it's stigmata, and the "blood" is said to heal all who touch it and give divine inspiration to those who don't. "The Righteous Thief" has been said to show holy powers as well as evil men have said that the statue talks to them and convinces them to at least give up their evil ways if not convert. Both are said to be in the Vatican Archives being studied.
"The Sinful Thief" however is a different story. The first recorded showing of it's evil was in the 16th century when it was accidentally separated from the other two statues. 11 churches around Europe were desecrated before anyone figured out the statue was present every time as mysterious cults, unsolved murders, and even the occasional orgy took place on the grounds. Thought to have been destroyed, "The Sinful Thief" keeps reappearing to spread it's evil through sacrilege, murder, and mayhem both sexual and otherwise. Last time anyone thought they saw "The Sinful Thief" was in the 70's when an Italian art student named Daniela Carcania claims that the actual thief of the statue would come to life and dismount from the cross to rape her, and did so repeatedly until she destroyed the statue.
Now, there's an old mansion in Cherry Woods, Pennsylvania. It's last owner mysteriously murdered in the 80's, his will has his mansion made into an art museum which displays his large collection- and the local colleges have been known to have field trips in which they are actually allowed to sleep in the mansion over night. These field trips have become rather infamous for their sexual escapades that take place, but this year a new statue has somehow appeared within the collection. . .
[Alright, so basically your characters have been locked in an old mansion with an evil spirit that lives in a desecrated cross. This spirit has been known to murder, rape, cause orgies, whatever.
I said EX because if the spirit is left alone with a man it will probably kill them, sorry fellas. Or if it amuses the spirit it may force the characters into an orgy. Or rape and possibly kill one of the female characters. Whatever it wants. And I'll be The Sinful Thief.