You play as the wizard Lucia. You and your friend Lena stumble upon the Sexonomicon while searching the mansion of a dead renowned wizard and decide to try summoning an incubus to have some kinky fun. Sadly the ritual goes bad and you end up summoning a powerful succubus. She gets pissed off at the girls’ dissapointment (who were overconfident that the succubus being trapped inside the circle couldn’t do anything to them) and tries to turn them into sex-crazed futanari minions but fortunately Lucia, being a powerful wizard too, has magic imbued in her clothes that deflects the succubus spell. Unfortunately, Lena does turn, she can rip her clothes and also her touch now turns anyone into an obedient sex slave. After getting her clothes ripped and briefly molested by Lena, Lucia manages to get back to her senses long enough to pick up the book, teleport to the attic and place a ward on the stairs.
After reading the Sexonomicon she learns that around the house there are 4 powerful seals that if activated should provide enough juice to send the succubus back to her realm. Of course, the succubus knows about it and isn’t planning to let her do it, so she sends Lena after her to stop her from activating the seals and to retrieve the book so she can dispel the summoning circle and leave the basement.