!!!SPOILER WARNING FOR SOLUTION!!!
So! Given this image:
The green square in front of the house
(this will be Sam's house, you can tell by the picture if you compare it) indicates where you want to start, and the arrows indicate where to go to find a secret item. You need to move your Farmer in the indicated direction until they can't go in that direction any further, and at the end, use your pickaxe to pick up the secret item. At the end of the sequence, you should wind up
behind Lewis's house and you will find
his secret art project...a golden statue of himself...
In the end, you have the option to return the item to its owner...but honestly screw him, it's a great trophy instead and only gets you 750g of hush money if I recall correctly.
Hope this helps!