Yes, Your Grace

You have to get 3 items .

A tooth:
In week 10 go in the dungeons, talk to the guard and get the tooth. Invite Lena to your castle and when she comes ask her about the tooth.
In week 27 there will be a small event with Cedani and the hunter and after that the Keep the monsters a bay achievement will pop and you will have your 3rd agent.
Ask the hunter to investigate the tooth .

A letter:
Go in the Bed Chamber and take the needles. Go in the gardens. There will be a crack in the pavement. Use the needles and you will get a letter.
Invite Grego and ask him about the letter. Ask the general to investigate for 2 weeks and get his response

A phial:
In week 17 you will get a mysterious letter and a hidden hut will appear on the map. Send your general there – it is important to do it in this week so make sure he is available.
After that a strange man will come with a request and a witch will help him. The witch will become your second agent and the Its time for magic achievement will pop.
The general will return and will give you the phial. Go to the council chamber and ask the which to investigate the phial.
The which will return. You will invite Lurs – if you have done the Etton achievement and didn’t reload this won’t probably work as Lurs is upset - and ask him about the phial.
If you want you can check the progress in the council chamber
After week 28 the trial will start and if you have done everything finally the achievement pops

A visual representation with commentary of the achievement in the video.