It's in Chapter 2 in Vergen. An elf tells you about a spree of gruesome murders and you piece together that it might be a succubus. When you do find her, she accuses the elf that approached you, as he fell so madly in love with her that he killed any other lovers she had out of jealousy. The succubus offered a different kind of 'reward' if I accused the elf to his commander, Iorveth. As a monster hunter I probably shouldn't have entertained it for so long and just killed it, but....I am a man. Kinky supernatural sex sounded too good to turn down. So I went to go about accusing the elf.
After examining one of the corpses earlier, all signs pointed to a succubus attack but there was something embedded in it's arm which you could only extract if you bought surgical tools from one of the vendors in town. Extracting it out reveals it's a metal fragment. So I went and accused the elf to Iorveth who revealed that the elf had fled town, confirming my suspicions. But not very far as outside the liar he was waiting for me and we had to fight. I won, naturally, and then I got down to her liar and then we uh....'sealed the deal'. Also got paid for it and got some epic armor as a reward too. Like a man should.
Kinkiness aside, it was a brilliant quest. It was a murder mystery essentially, and it was long, varied, required you to think and had brief spells of combat. Funny too, like when you have to play as Dandelion and make up the poem. Or when you make Dandelion go down into the liar and it cuts back to Geralt. "That fucking idiot!". Saw how it played out if you killed the succubus instead and the rewards are different as well but equally worthwhile getting. Although I am much happier with the armor. I needed an upgrade but couldn't afford one, and this armor not only give me improved stats on everything but also increases my bomb damage by 50%. Very, very useful.
