As Thorin, Gandolf, and Fosco peer into the next chamber, there is a strange, alien noise and two somethings from above, like two long/slender spider's legs, strike down, one impaling the wizard's apprentice (4 damage) and the other seizing the dwarf by the neck, hoisting him up off the floor. Fosco shrieks in terror as something monstrous falls to the floor from above, screeches in a loud voice "Please! Don't hurt me!" and then strides away into the darkness in the blink of an eye, dragging the flailing dwarf who would scream but for the tight claws squeezing his throat shut.
Surprise round over, and the monster fled (through another archway immediately to the north on the other side of this open archway), so no need for initiative.
Fosco's terror abates and he regains his wits.
(GnomeBoy, you can post the drawing whenever you're ready...