I found out about this story series today after coming across these TF sequences:
http://g.e-hentai.org/g/905976/507a9d5e17/
http://g.e-hentai.org/g/910989/1e104fbc95/

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Synopsis:
Carl Treynor, a xenobiologist sent to study the strange life forms of an alien world, discovers a form of lust never before seen by man. Will he succumb, and give in to his own desires, or will he put his fellow man first, and prevent this strange new life from ever reaching another human being?
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It's actually running on a decent plot too. The whole story can be found here:
http://www.hentai-foundry.com/stories/u … ion-Desire

You can click on the PDF icon to download it as a PDF with all 20 (so far) chapters.