This achievement is story related and will be unlocked during natural progression. To know when it will pop specifically, please see spoilers below.
*** Spoiler - click to reveal ***After speaking with Bluebeard about Crane meeting a witch for black market glamours, Snow will ask Bigby where to go and you will receive a new objective to "Find the witch". Bigby then walks over to contemplate the decision and you must choose between Dee's Office, Crane's Apartment and Holly's Bar. Regardless of your decision, there is some brief dialogue, the screen fades to black and the achievement will unlock.