Hello! Before you check for the secrets, please note that I have spent many hours looking for secrets and went 3 times through the game. Therefore, please consider rating this guide :)

Getting all the hidden things will give you several achievements:

To the last cent!
You need to find all the hidden money to get this achievement.


Professor mask!
You need to find the Professor Gustav mask to get this achievement.


Mayor mask!
You need to find the Mayor Wilson mask to get this achievement.


Jackpot!
You need to take the jackpot to get this achievement.


Banker mask!
You need to find the Banker Byrd mask to get this achievement.


A bloodhound's senses!
You need to find all the secrets to get this achievement.



Also, you will earn enough money to buy stuff for your garden.

Connoisseur!
You need to make your first purchase in the garden to get this achievement.


Decorations all around!
You need to make 10 purchases in the garden to get this achievement.


Beauty will save the world!
You need to purchase everything in the garden to get this achievement.



About the keys used in the pictures below:

Yellow spots count for Hidden Money. /!\ MOST OF THEM ARE INCLUDED IN HIDDEN OBJECT SCENES, AND THUS, ARE MISSABLE /!\
Orange spots count for Hidden Money and Secrets (20 in total).
Green spots are for the 3 masks.

Why no plants? For many reasons:
1) They are really EASY to find.
2) You can't miss them unlike money spots because they are not included in Hidden Object Scenes.
3) There is already a steam guide for them.