Go to Berith
Its point on the map looks like this:


The Berith itself:


After you visit it, you will be given a drawing of the atelier for the first time, it costs 16 cobwebs and 8 gold bars, you can make clothes and modify them in it.
Then take a costume pattern from him, it costs 10 gold bars, make more of these costumes and throw them on your followers. The spies themselves will appear in standard clothes (please note that personal suits can be sewn once, so this is a bad option), after you dress up your followers, change the standard robe that will immediately catch the eye.
This is done here:




how it will look like:


Examples of cheap clothes from Berith:





P.S. if you have add-ons for costumes, then it's even cheaper and easier since there is a costume made of colors that is immediately available.
Here he is:


(I noticed it while I was adding screenshots to the guide. some of the colors are not original, but modified by me.)

The atelier itself:

Check and keep track of the number of followers
You can view it here:

If their number has increased after the Crusade, then check for spies in the settlement.

How do I make sure that I have a spy in front of me?
In order not to accidentally kill a loyal follower (or one who is not very loyal), be sure to read the thoughts and look at the features.

If you've found this trait, then you've got a spy in front of you

They can be easily identified by their behavior.:
1. They will release prisoners (if any), but keep in mind that if a follower has a trait of contempt for the law, this does not mean that he is a spy.
2. They'll look around a lot, so keep an eye on their faces.
3. They don't work, or rather they pretend to work and don't do anything useful for society at all, they don't even write poetry!
4. They often quarrel with other followers.
An example of a spy:

There will always be one spy, there can never be more than 1.

Make your followers stand out in appearance and color.
It is best to use the looks of the bosses and the pink color, then the spy will stand out very much.
This option is actually not very good, as you will have to sacrifice the individuality of each follower, and children and characters like Yarlen, Rinor and Jalala will not be able to adjust the color, but the method does its job perfectly.

How it will look like:


Who doesn't know how the follower is configured:

Appearances:


Colours:


How it will look like:

(Don't pay attention to the halo)

(yes, you can change appearance of your follower, but only after you open the re-indoctrinaition circle and it will cost 1 sin)
re-indoctrinaition circle:

Spies appear in the settlement with a random probability and stay in the settlement for 5 days, after which they steal 10% of all your money, so it's better to get rid of them quickly.
There are many ways to do this.

1.The simplest and most radical: if you have the opportunity to kill followers, then you can do it on a spy (the main thing is to do it at night and without prying eyes).

2. Simpler and more useful: sacrifice him. It's certainly not free, but you can get loyalty or money and lose a little faith if there is no "Belief in Sacrifice" feature


3.Ascend him: it costs the same as the sacrifice, but you do not lose faith and after several ascensions you also receive meat and the level of loyalty of the followers increases greatly.

4. Arrange a ritual duel:

not the best option because a spy can win a fight, but if he loses, press your finger down, thereby killing him.
Where to click to kill:


5. The worst option for me is that you will need a Gluttony of cannibals for it

why do I think this option is bad? Because -40 faith is too much, and you won't get too many sins, and it's expensive.

6. Prepare a deadly dish. this is not a bad option, since after death spy can leave useful materials, just make sure that he is not eaten by your followers.
Here it is:


If you see a follower, or rather a spy, heading for the exit of the settlement, you can say goodbye to your money, because you will no longer be able to interact with him!

P.S. you can resurrect spies after you kill them, so be careful.

Thank you for reading my guide and I hope it helped you!
If you have any ideas on how to figure out spies or questions, write them in the comments, I will read everything!
Good luck to you and bring kindness to people!