When a group of alien mermaids led by Taija Rae finds that the Earth's water is too polluted for their health, they need to leave...pronto. Unfortunately, one of their kind, Vanessa D'Oro, is enjoying the sex on the planet far too much to join them, despite the fact that it will mean her demise. So, as any good alien mermaid leader would, Taija seeks out the help of the rough-around-the-edges good guy, John Leslie--who's apparently a "mermaid whisperer" of sorts--to help. Such is the case in "Talk Dirty to Me 4", an overall-good, 1986 release from Ned Morehead and Dreamland Entertainment.