delericho
Legend
Plot device events need to happen off screen. What is the point of having the PC's jump through these hoops to get to a location in time when the end result would have been no different if they took a lunch break and strolled over to the vault afterwards. This is the textbook example of pointless encounters. If the end results of the encounters don't matter then why play them out?
Indeed. Also, if an event must happen, then it really needs to happen off-screen. PCs have a nasty habit of doing things that break the plot, like preventing the key theft/murder, killing off a crucial NPC at a bad time, or whatever.
And if the PCs literally can't affect the outcome, then you've got a whole other mess of problems. It's railroading to some extreme - take it too far and the DM might as well just read the story he has written to the players.
(Still, could be worse. In "Expedition to the Demonweb Pits",
the PCs are given their mission by a key NPC of questionable character. Immediately before meeting said NPC for the first time, there is an encounter in which the PCs are directly warned not to trust this NPC. So, the entire plot is contingent on the PCs foolishly trusting an NPC they've just been warned not to trust?