Here is the full list of all 28 Echoes of the Fey: The Fox's Trail achievements.
Manage to keep the secret you discovered entirely under wraps
Conspire with the Imperial presence in Vodotsk to protect a secret
Uncover a new layer to the case
Lie to your client rather than betray another's trust
Complete the third day of your investigation and close the case.
Talk the fire mage down at the Krovakyn Church
Get close to Viola right before a crisis
See all optional scenes with Kazamir
Tell your client the truth you have discovered
Complete the second day of your investigation.
Uncover Folren's fate by piecing together the clues yourself
Find out what happened to Folren from Eduard
Spy on someone during an optional scene as a cat
Complete all optional side scenes with Eduard
Ask all optional character questions.
Complete all optional side scenes with Heremon
Forgive a friend for a betrayal of trust
Take a risk with an unknown potion
Complete the first day of your investigation.
Complete all optional side scenes with Luka
Give Luka the correct answers during your interview
Complete all optional side scenes with Arkady
Listen to one of Simion's Leshin fables
Purchase and read one of the books from the bookstore
Forge your name in the appointment book of the low mage
Purchase and use an optional costume change for Sofya
Ask a full set of questions during an interview
Anger Tiatha and impress Heremon by avoiding a troubling case.