This is why I often just write down a series of truths I want the characters to discover instead of coming up with exact clues. Then no matter which direction they go in I can place those truths.
Let's say the characters are investigating the death of a powerful merchant lord. I might write a list of truths like this:
- The merchant lord was killed by a werewolf.
- The werewolf is Baron Wolfson.
- Baron Wolfson was cursed by a witch.
- The merchant lord was exploring magic from a faerie glen.
- The witch cursed the Baron to kill the Merchant Lord in order to protect the glen.
Let's say the characters go to talk with Bob the Commoner. I'll look at my list of truths and either choose one to reveal, or Bob will point them in the right direction. Or better yet, both!
DM: Bob shakes his head, hearing of the grizzly details of the murder scene. "Whenever something goes wrong around here, we usually blame the Witch of the Woods. She's always causing mayhem to anyone who goes near her Secret Glen... I have no idea what's in there, and I'm too scared to find out!"
Now the characters have learned that there's a witch who protects her secret glen, and they have a new place to explore and learn more!
But maybe they take a left turn.
Players: Secret glen? That reminds me, I wanted to ask around at the tavern.
DM: You ask the regulars at the tavern, but they're all as lost as you. However, you notice that a bard is singing a melancholy melody about a Witch's Curse... A woodsman in the song is cursed by the witch to take on the form of a wolf and attack his fellow woodsmen."
Now the characters can talk to the bard, or go find the witch, or look for wolf tracks... And the adventure goes on!
I'm also not afraid to connect the dots for the players once they've uncovered enough clues.
DM: Reading over the journal of the Captain of the Guard, you find out that he saw the Baron walking out of the keep under the full moon... The captain went to find a lantern, and when he looked back the Baron was gone. He heard a bone-chilling howl. You realize that, of course, the Baron was the werewolf who attacked the Merchant Lord! And that the witch must have cursed him in order to protect her secret glen.