It was All Hallow’s Eve, the one night a year when demons from Hell like you were allowed to freely enter the mortal realm and walk amongst the living.

No, not because of any supernatural reason, but because everyone thought you were all just normal people in costumes.

This Halloween you were invited to a party at an abandoned human mansion and arrived to find it filled with all manner of demons, imps, hellhounds, succubi, etc, all laughing and chatting and drinking and such.