I got stuck near the beginning. I feel a bit silly, because I looked up in a walkthrough the next step to follow, but it doesn't help.
Spoiler
I stole the shoehorn, but then I didn't know what to do with it. The walkthrough says "leave the shop and use the shoehorn on the trapdoor on the right to go underground," but I don't see any trapdoors, or any other thing that could resemble a trapdoor, or anything at all I could use the shoehorn with.
Thanks!
The you probably didn't follow it correctly. The walkthrough also says before that:
Spoiler
Use the magnet on the guard to search for lead items. Use the magnet on the ground in front of him to discover a hidden passage.