My idea is to take futher what we saw in the jiology lab with jia and veronica leal. A girl gets infected by a parasite(it can be in many ways an alien plant for example) and her only mission become to bring a girl to mr alien. She founds a girl and infects her, so she can easily take her to mr alien.
Mr alien starts to have sex with second girl and after getting horny for watching them also the first girl join.
Mr alien starts to have sex with second girl and after getting horny for watching them also the first girl join.