1.) In the first scene, find the potion and drink the wounded gribler, he will give out the sword.
2.) Kill the guard or steal the key and get on the scene the prison outside.
3.) There, find a nut and feed the captive gribler, ask him to raise a riot.
4.) Open all cameras and kill all guards
5.) Having come to the sewer, you need to find a stone and throw a stone into the web.
I've tried the same thing. I can't get anywhere. I followed the steps and this is how:
Look around. Got Potion. Drank Potion.
Wait until the slugs are gone. Ask "What's happened to you?"
Steal door keys. Look around. Offer acorn to gribler. Ask him to arrange a brawl.
Open all the cameras and attack the guards. Look around. Get stone.
Pass stone into the spider's web.
Rusty dies. Again. What next?