Claire is lying on a back alley, bleeding and dying from a mysterious attack. As she is about to pass away, a vampire comes to the rescue by making her into one of his kind. Now Claire has to stalk the streets of Boston, searching for her murderer while fighting to stay as human as possible.

Nocturnal: Boston Nightfall is a standard hidden object game with mini-games between chapters. The main objective is to find all the objects listed at the bottom of the screen, on locations cluttered with scattered and assorted paraphernalia, within a time limit. Wrong clicks take away six seconds from the clock. The timer can be turned off at the main menu.

One of three mini-games appears after each level: a concentration game with cards, a Simon game with orbs and a Master Mind lock-picking game. Some of these games can be played over again to get extra hints. The hint button highlights the position of one of the objects.