Have you read Peter Watts's Blindsight?

He really SELLS the "vampire in space" thing.

No, I haven't, but it sounds like he earned it, so to speak. Yes?

It edges out Brian Stableford's Empire of Fear and Scott Weterfeld's Peeps as my favourite semi-biologically-plausible vampires.

Which is to say, yes. It just automatically leaps to mind with those particular combined tropes...

YES! In fact, it's not the "impossible thing." As a biologist, he comes up with a completely plausible, if somewhat wonky, backstory: they used to exist and were a predator to H. sap's prey; they weren't sunlight averse, but they hunted at night and had great night vision; they died out when we discovered technology because they had a "glitch" in their visual cortex-- the wiring made them hellacious fighters, but sharp, manufactured angles screwed up their vision, gave them seziures of varying intensities, and made them highly vulnerable.

The "freebie" he asks you for in the book is much harder to swallow... at first. And when he plausibly makes the case for it, you're reaction is "Oh, crap... we are all f'ing doomed."

but, but, but, what about Lifeforce?

I think of it slightly differently, including the flying snowman part. You get a grace period at the beginning, when you are establishing your world and its rules. If you throw something else at the reader after that window has closed, it's going to be a flying snowman.

David Weber's alien invasion novel Out of the Dark is one of those that tries to get too many impossible things into it. Galactic Hegemony, alien invasion of Earth -- he gets credit for those, and for other things as he builds the story. But near the end, he throws in vampires and Vlad the Impaler. Completely blew the novel because he'd already used his allotment of impossible things. (It was also a Deus ex machina, which also contributed to the failure of the novel, but that's beside the point).

It did not fail completely, in my opinion, because Weber had at least conventionally-foreshadowed the introduction of the vampires. However, he could have done it better -- perhaps by having some character suspecting their existence towards the beginning of the tale, or in some way linking his technological with his supernatural speculations. Compare with Lumley's "Necroscope" series, which fairly well integrates the Cold War, psychic powers, vampire, alien dimensions and the Cthulhu Mythos.

Plenty of science fiction comes with FTL travel, strong AI and teleporters all at the same time, for example. But in a sense, those are all one thing. Say, the starship Enterprise.

Or, to put it another way, Federation technology. Much of which is based on common principles (and where it wasn't, as with the transporters, later writers retconned it so it was: note the role of the "pattern buffer" which is based on the existence of powerful computers.

One can have all sorts of inventions wondrous from our POV -- one will, in any plausible future other than one of complete civilizational collapse (think of what we routinely use today, from the POV of 1912, including this website). But they will all fit together in a common technological system -- and anything which doesn't should be a major point of the storyverse (for instance, if one had a Victorian-tech interstellar empire using relic stargates, or something like that).

What really destroys a story is when new technology is just thrown in to meet the requirements of the plot. I've recently been reading a lot of early-1930's pulp sf and I've noticed this happening a lot -- the worst offender so far is a Hall air-war story set in the Near Future of the 1940's in which -- in order to force the protagonists to go on a suicide mission to save America from the "United Slavs" -- it is revealed that we have secretly developed exoatmospheric cruise missiles driven by gravity-warp engines, equipped with stealth technology and armed with gigaton-range warheads. At no point is the author (or any of the characters) apparently aware that any ONE of these technologies, by itself, would be enough to win the war. Instead, they are all mentioned in the context of the Heroic Suicide Mission and with precisely the limitations required to conform to the shape of the plot. This is simply bad world-building.

Contrast this with another writer from the same era, E. E. "Doc" Smith. His stories are similarly technology-driven, but the difference is that "Doc" Smith constructed coherent science-fictional systems of physics for each of his storyverses, and the devices which affected his plots were (reasonably) logical outgrowths of the hypothesized physics. Half of the joy of reading his stories is participating in the process of discovery that leads to these devices -- Smith would often have viewpoint characters who were scientists, engineers or (in Kimball Kinnison's case) highly-educated paramilitary charged with applying these devices who also participated in their development).

Humans are pattern-seeking creatures, and we notice the difference between a pattern maintained and a pattern violated, even if we aren't consciously-aware of our pattern-seeking. We experience patterns maintained as "harmony" and patterns violated as "dissonance." Hermony is pleasurable; dissonance is enjoyable only when strategically-applied to break harmony at the right time and in the right manner (hence, the space vampires could work if done correctly).

When I was an adolescent, I noticed that I enjoyed reading "Doc" Smith more than I did many other writers from his era: I didn't know why, but Smith's superior harmony in worldbuilding is why his stories are still widely read today, while many other authors are now still read only by fans of the obscure, like me.

One of my longer WIPs is a very nice hard science space opera with vampires.

No, seriously.

Dr. Phil

My take on it is somewhat different. I think what happens is that people are reading/watching a work, have the thought, "I'm not buying this" and then start looking around for why they're not buying it. So they find plot holes and implausible science and vague world building and say, ah-ha! That precise thing is why I am not buying this!

But I think usually what happened is they got a little bored.

Except for that -- boredom -- I would never try to come up with a unifying principle of how to keep people from falling out of your story, because I think it's different for every story, and every reader.

For example: one reason *I say* Twilight doesn't work for me is the vague world building. I think she mashed vampire tropes together without thinking about the implications. Her vampires are too indestructible and too easy to create -- I don't buy that there would be so few of them, and I don't buy that they would fear discovery by humans.

But I think if the underlying story worked for me, I wouldn't spend any time worrying about that.