Maybe It's Happened Before and We Just Didn't See It.
During the previous battle, we saw some villagers being dragged away by Invisible Stalkers. We saw them because we had a See Invisibilty spell active, obviously. Now we think that perhaps we should do something about the Stalkers, to prevent more villagers from falling prey to them.
Rather than rush in, it's probably best to get an idea of where we're going. 'What can I find out about the valley?'
'Make me a Gather Information check.'
'Uh... 3.'
'You know that it is lower down than the mountain, and roughly in that direction.' Excellent. Let's go. Well, after a good night's rest, so that I can learn a couple of See Invisibility spells. They will be handy, but as the journey takes the best part of a day and the spell lasts only 10 minutes/level, we can't rely on them.
Thrak has an idea to help with that, though. 'We'll keep an eye on each other to see if anyone is dragged away by something we can't see.'
It's not a bad plan, but I can't help but think that we don't really need to state it. Don't we do that normally?