You slip into the crack to the Big One's right as it closes the distance. For several moments, you hold your breath as the stamping footfalls get closer and closer.
You can hear it's breathing now. It's different than the hissing of the smaller ones. It sounds more like a bellows that keeps a blacksmith's fire roaring. The cadence is out of sync with the steps, which makes it all the more jarring.
You grip the spear with both hands and try to picture its head height. "Aim for the eye," was the advice you got. The creature stops before coming into view, and you feel the sweat break out on your brow. You wonder if it sees you, or perhaps smells you.
The creature stands there, breathing, then continues forward again as before, moving at the same pace as if nothing had happened, but you don't let out your breath just yet, not while it's this close.
The eye appears lower than you thought, closer to your stomach than your shoulder. You quickly adjust your angle of attack and lunge forward. The strike is swift and true, and the creature falls to the ground, dead, before it even knew you were there. Your heart is racing with victory as you quickly look around to see if any there are any other lizards. You think you may hear some hissing in the distance, but otherwise all is quiet.
Running back, you start yelling out happily. The men at the gate hesitate to open for you at first, thinking you're being chased by a hoard of lizards, but you are able to explain to the translator what happened. The Princess is summoned, and you then lead a contingent back to the body to examine it, and be sure it is dead.
When the Princess sees what you have done, she is overjoyed and calls for a feast. Scouting parties are sent out to see what has become of the lizard army, but without their leader they appear to have fallen apart, and disappeared back into the cracks and deeper places within the tunnels. As such, no assault ever comes. Caverns lost to the lizards can be reclaimed, save for the one you were in that was destroyed.
There is much dancing and rejoicing, and it's all for you. Your bravery ended the war and saved many, many lives.
The End.