[@Lucius Cypher]
Orchid will have made it to the top, it was about 40 feet of climbing. Let me make some basic trigonometry to find the distance. For simplicity, let us assume the dragon's current flying height is approximately equal to the height of the tower (while it really flies a bit higher, but I am no mathematician).

As per the Pythagorean theorem, in a right triangle we can find the length of any side through a[sup]2[/sup] + b[sup]2[/sup] = c[sup]2[/sup]. In our case, c would be the distance from the rest of the party (100 feet) and a would be distance to the top of the tower (40 feet). Thus we will have to find b.

40[sup]2[/sup] + b[sup]2[/sup] = 100[sup]2[/sup]
1600 + b[sup]2[/sup] = 10000    || - 1600
b[sup]2[/sup] = 8400    || take square root
b = ~92ft.

That would mean that b (the distance between Orchid and the dragon) is roughly 92 feet, a wee bit far to fling harpoons. Also, if I use any terms that are off, please excuse me. I don't speak science that well in English, given all of my education has been in Finnish.