This was an issue facing Iron Man 3, where the decision was wisely taken to assume the whole world had seen Avengers and knew who Tony Stark was. But what to do with a new Star Trek film? Can you assume so many people saw the first of the re-booted series that you can do without back story? Do you bank on the army of TV fans going with you to the big screen, even though you've re-written the history a smidge?
Seemingly, the answer is yes. So if you haven't seen the 2009 incarnation, you might want to do some homework before tackling Into Darkness. You don't need to know what happened, but it helps.
For the uninitiated, here's a quick recap - Chris Pine is now Capt James T Kirk. His dad died in action just as he was being born, and he got recruited into Star Fleet by a kindly Capt Pike (Bruce Greenwood), who becomes his mentor and saviour. Spock, meanwhile, is now Zachary Quinto, and Vulcans are now an endangered species after a Romulan with a grudge took out Spock's home planet. Got all that? Good.
Oh and Spock's getting it on with Uhura (the wonderful Zoe Saldana). But everyone knew that, right?
This time around, Kirk is on a mission to capture a rogue Star Fleet agent (the sublime Benedict Cumberbatch), who has decided to essentially declare war on Star Fleet. From here, friendships are tested, lives put at risk, things blow up and classic lines are uttered. All in 3D. It's a complete geek fanfest.
And that is a very, very good thing. Even the 3D.
Now, granted, if you don't know what Star Fleet is, or the Prime Directive, or that Spock is half-human and now technically homeless (well, half of him is), you might struggle a little bit to keep up - but is there really going to be anyone going to see this film who doesn't know all that?
Probably not, but it's still a risk when you basically pick up where the last one left off.
For the card-carrying Trekkie, however, Into Darkness has something for everyone, with its past being quietly acknowledged (there's a Tribble. A bloody Tribble) while the past is neatly tee'd up once the dust settles.
And this is, ultimately, the best of the series. Better than all of the original ones. Better than all of the Next Generation films. And better than its predecessor.
For a start, there isn't a bad performance to be had here - with Simon Pegg's Scotty arguably stealing the show. From being a more marginal character first time round, Pegg is at the heart of this story, getting involved with the physical action as well as being up to his ears in warp cores. Then there's Alice Eve (daughter of Trevor, star of She's Out Of My League), who joins the Enterprise crew as a new science officer. Gratuitous shot of her in her underwear notwithstanding, she more than holds her own among a cast who have already established themselves as the new frontier of Gene Roddenberry's universes.
The lines are sharp, the humour honest and well-placed, the score is not overly intrusive... and it has serious emotional weight and punch. As the final scenes unfold, you'll find yourself leaning forward and holding your breath. You've come to know and love these characters, and you care what happens to them.
It's a film about trust, friendship, honour, love, family and squabble in a small ship - all of which combine to make Into Darkness a pretty damn-near perfect addition to the Star Trek cannon.
Which is, for me, an amazing achievement when you consider it was shot in 3D.
Now, as I may have mentioned before, I'm not a fan. When done well, it can be interesting. Or, it can be Iron Man 3. But director JJ Abrams pulls it off with aplomb.
Normally, it's used as a gimmick. Things whizz out of the screen at you randomly while the rest of the film just looks normal, but from the off Abrams uses it to add the depth the pro-3D lobby insist it provides.
When we meet the Enterprise crew, they're trying to stop a planet being wiped out by a volcano while running away from the natives. Spears are flying at you, past you, around you, ash is falling, and it all looks stunning. I haven't been this impressed with 3D since Avatar (yes, the film was snoringly dull, but it looked fantastic). I even ducked at one stage.
And as the film unfolds, and the action moves from earth to space and back via sundry other planets, you are so immersed in what you're seeing that the glasses are not even noticed. Which is no mean feat.
Part of the trick is how Abrams has coloured Into Darkness. Where the glasses inevitably darken the screen, Abrams has gone for starker, bolder colours, meaning the richness of tone is preserved. And the action scenes aren't, for the most part, compromised. One of the issues with 3D is how, in the fast-paced scenes, things can blur, but that's not an issue here. The only negative comes in a fight scene towards the end, where the darkness does cause you to wonder who is hitting who, but that's so far into the film it's only a minor quibble.
The one place where it does fall down (and it's not Abrams trademark lens flare styling, which actually benefits from being damped down here) is a few scenes where things are in the foreground and so blurred. Your eye is inevitably drawn to the splodge down the front, detracting from the main scene (hospital and bar scenes are the main offenders, and a red flashing light in a corridor which almost became a character in its own right), but these really are the only issues in a little over two hours. Which must be some kind of record.
This film will be a hit, of that you can be sure - the first film and its heritage will see to that - but it deserves to be.
The modern blockbuster is fast becoming a vacuous, empty experience (yes Michael Bay, I'm looking at you), but Abrams has joined the ranks of Christopher Nolan and Joss Whedon in introducing brains to the mix.
Star Trek Into Darkness will make you laugh, make you cry (possibly, no spoilers here sir...), put you on the edge of your seat and throw you back in your chair. It is, in short, a geektastic feast of visual delights.
PS - To make sure you get the full impact of the twists and treats here, don't go looking at IMDB until after you've seen the film. The cast list is a spoiler in itself.
PPS - Enjoy this, we did: