The mystery hook requires active participation on behalf of the characters because their enemies aren’t (yet) looking into them and so if they persistently ignore the hook the campaign will fall apart. Therefore it is important to have the players on board first and foremost. If they are the type who hate doing something that wouldn’t make sense for their character, make doubly sure they have characters built who would take the bait.
The trick with a Bizarre Mystery is to take the initial situation and make it odd enough to inspire attention. It can help to have a second hook in case the first doesn’t provide sufficient incentive. Perhaps after the mysterious letter, they find a mysterious break in as someone steals the letter. This is still not a Sudden Event hook because it happens while they are away and if they simply file a police report and ignore it than there will be no further pokes from plot.
So make it interesting and tie it into the characters as best you can — both through nudges in character generation and through adjusting the hook to suit them. The Pathfinder campaigns often encourage players to select campaign traits that provide in-built motivation. You could borrow a page from their book to nudge die hard character immersionists into having the incentive to follow the plot line. Sample traits could involve an interest in local history or a desire to be an amateur sleuth. It doesn’t really matter so long as it helps ensure the characters get involved.
Once involved, the characters need to behave proactively for the first section of the game until they draw enough attention to themselves for the villains to put them on the defensive. If you’re curious about seeing this sort of hook in action, take a look at the grand majority of Call of Cthulhu games where the character hunts down a particular clue thread until they surprise the evil villains in the middle of their ritual. Naturally if it’s a campaign the situation might not remain so proactive throughout but it is important to bear it in mind that to begin with the PCs will control the pacing unless you put in an obvious ticking clock.
Do you have any advice for baiting a mystery hook? Seen it done particularly well? Feel free to put down more ideas in the Comments section. Alternatively if you’d like to check out the base article you can learn more about other forms of campaign hooks.