I...uh....wait...ummm...hold on....wait...

"you feel the spell take hold, but for some reason the crown remains rusty"

Then you pivot that the rust is a powerful illusion or some kind of curse cast on the crown by someone related to that backstory to keep it hidden. Then while your players try to figure out why simply cleaning the rust didn't work, you try to figure out how to weave in that backstory sooner than later.

If you're really not ready for it to happen, make sure they have some other quest to do that has a pressing time limit.

you're definitely right about the time limit. at that point you are about 5 minutes away from every spell in the party's arsenal being cast on that crown, followed by the main quest getting derailed by the mystery of the plot armored artifact.

Thats DnD, though. You're not the narrator, you're the benevolent god allowing the story to unfold.

I played recently with a newer DM who had written this complex story and kept trying to weave in obvious set pieces for us. At first, I played along, but when we started to go off track, he introduced an omnipotent NPC to help keep us on his path. I was done at that point. I'm not here to listen to a story.

If I find a clue early, I understand it might not make sense until later.

Twist: You think this is the legendary lost crown of Foo? Some rotten trash you grabbed in a dungeon just happens to be the thing you've been looking for all this time? Pull the other one! It's been so ravaged by time that none of the markings or engravings are clearly visible. Best you can hope for is that some merchant will buy it off you for scrap.

Even if the PCs think this is the lost crown of Foo, only the kingdom's last grandmaster artificer can conduct a conclusive test. Assuming you even find them, it's not like they take appointments from any dirty old adventurers off the street.

Going by your entire comment alone.

I have juuust the right youtube video for you: https://www.youtube.com/watch?v=EkXMxiAGUWg

I'm extremely naive when it comes to tabletop RPGs

Is there any kind of "plot says no" response to magic? Something like the doors in oblivion where you need a key to unlock

Really, what the DM says goes. So if you want to be boring you can just say it doesn't work for some reason. The answer above re: pivoting to it being a powerful illusion spell or something so there is a reason the spell didn't work is a lot more compelling and interesting imo

That makes sense! I've always wanted to run a campaign (even though I've never really played) so I try to take guidance from stories like these

Thank you!

there's two answers to this question, one is mechanical and one is social. you as the DM can tell the players no not now, and they can't do anything about it, but that doesn't mean they won't try to do something about it, which depending on the group could be an issue.

so in this scenario a good DM could whip up some misdirection, for example set up a traveling artificer who just passed through town a couple weeks back and who the players could track down as a lead - conveniently in the direction of the main quest objective.

this is hard to do on the spot.

We don't do that here. The GM provides the model of physics the players accept and expect. If the GM just says "nah" when stuff is inconvenient, players don't know what to expect, and the world becomes inconsistent.

A big part of the GM's fun in TTRPGs is improving off that. Players always ruin my plans, but that's part of the game.

You could also just have it work and go with whatever follows from it though.

I believe you should have a plot prepared but you also shouldn't be afraid to adapt it if the players do something unexpected.
It's more work, but in my experience players can usually smell when you're just trying to block them. And they will derive fun from having found out your plans early (which is totally ok to tell them).

If you've railroaded your campaign that much you're a bad GM. It's not your story, it's your players story.

Having your complex plot get fast forwarded because of a cantrip, priceless

"You can certainly try"

Ime, players are entirely willing to accept an extremely short session just so I can prep and set back up after they throw me a massive curveball. If you're capable of doing it on the fly, that's great, but I'm not and my players usually understand.

Had a twelve minute session once because I forgot I gave the party a foldable boat like three months ago on a whim, and they used it to skip the next ~3 sessions of content. I had an entire thing setup where they'd help a dwarfhold hunt a dragon, and had started on some city-based intrigue in the next area.

I just leveled with them that I had not even slightly expected this session to go this way and had nothing prepped so we'd stop early and pick it up next time.

The crown completely disintegrates, as it was rust all the way through

Sorry, Mario, the real crown is in another dungeon.

I once fast-forwarded a complex plot through a GM-sanctioned bit of fluff.

The party had been invited by their uncle who turned out to be recently murdered when they arrived. Of course they investigated. At one point I had my character wrote a letter to the rest of the family to inform them of what was going on. I actually produced the letter as a handout. Since I had no idea about the date I asked the GM and he told me to pick anything in summer.

The GM s happy with the handout and it was deemed canonical.

A few sessions later he noticed that I had picked something ahead the end of the summer and the bad guys' plot was about to kick off at a specific date right after summer ends. So suddenly the adventure went from "careful slow-burn investigation" to "mad rush to the location of the finale".

Oops.

Couldn't they have gone the other route and made the villain's plans a year later? But sounds like it was a lot of fun the way it was run!

The idea was to have some kind of urgency but only once the players were far enough to understand the basics of what was going on. To that end, the date was supposed to be vague so that the GM was free to say "you figured out that the ritual will happen right after summer ends – which is in less than a week".

Then he forgot that the timeframe was vague when I wrote the letter and told me to pick a date.

Unfortunately, this cut out a side plot where our party would've hired another party to hunt down some artifact. That artifact retroactively got downgraded to a red herring for time reasons.

On the other hand, we got an absolutely precious scene where the one party member who wasn't magic-affine and didn't want to be involved with any supernatural stuff had to ride an unnaturally fast six-legged half-demon horse in order to catch up with the bad guys.

Also, it cut down on all the "three wizards and a vintner have breakfast and discuss the state of the investigation" episodes. We had a lot of those.