At the back alley, right from the Finman's, Pesce tells Don can enter only in the presence of chief Piovra.
By the way, if you can't leave the scene, save and exit and change your resolution. The exit arrow will become visible. This is a known bug in the scene with Pesce.
This is the low-spoiler guide for "Finding Chief Priova" puzzle in Gibbous - A Cthulhu Adventure. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.