Quickbeam says that there is little more he can do until his kindred decide upon some course of action...but he believes that he has found a way for you to enter the fortress of Isengard undetected.
'You want to find a way into Isengard? Hoom. Well. There is no way one such as I could enter unseen, but you are so small, little ${RACE}, it seems that you could slip in through the cracks in the stone!
'Perhaps I can help you there. I saw a small stream made by the hands of Men coming from within Isengard. It carries the stench of fire and iron, so I suspect that you can find your way inside along it.
'Meet me down by the edge of the river below, and I will show you the way.'
Quickbeam is at the river's edge, down in the Vale below his home.
Quickbeam has asked you to meet him down by the river's edge, where he believes he has found a way to sneak you into Isengard.
You should sneak into Isengard through the tunnel Quickbeam has opened for you.