Seriously, though, this story explores the human capacity for sexual desire and the destructive effect that it can have on us as a whole. It's also very, very funny. It's the story of Enoch Mirren, temponaut, who returns from his trip to an alternate earth in a very, well, strange way. Let me let Ellison explain it:
"When they unscrewed the time capsule, preparatory to helping tmponaut Enoch Mirren to disembark, they found him doing a disgusting thing with a disgusting thing."
Mirren, in his travels, has come accross a being called a Cissaldan, the perfect sex partner, and is now locked in neverending coitus. Unfortunately, once those in charge finally figure out a way to pry Mirren and the Cissaldan apart (it's not easy: they even try pulling them apart with horses) and find out what has happened, it's already too late.
It turns out that Cissaldans, never having come across other sentient life before, have, until now, have only ever been able to have constant sex with one another (they're apparently very good at it). Understandably, they've gotten a little bored. So, when they get the chance to schtup a new life form, they take it. The Cissaldans, despite being rather disgusting amorphous ball-like things, also possess psychic powers and the ability to produce powerful hormones, so, it's not like people (or anything) can resist. The apocalypse, or the world's biggest orgy, depending on how you look at it, ensuses.
Setting aside Ellison's basic assertion that, given the chance for perfect sex, humans will give up all else, including eating, sleeping, and, ultimately, their lives, and what that might say about humanity as a whole, this story is mainly just pretty funny. Especially the lengthly section in which Ellison describes how various celebrities and political figures of the early 1980s are overcome by the Cissaldans. My personal favourite being the description of William Shatner, which is as follows:
William Shatner, because of his deep and profound experience with Third World Aliens, attempted to communicate with the disgusting thing that popped into existence in his dressing room. He began delivering a captainlike lecture on coexistence and the Cissaldan -- bored -- vanished, to find a more suitable mate. A few minutes later, a less discerning Cissaldan appeared and Shatner, now overcome with this good idea, fell on it, dislodging his hairpiece.
And, if you don't think Ellison thinks highly of Shatner, wait until you read what the Cissaldans do to Anita Bryant.