This is an expansion for Arkham Horror Third Edition.
Description from the publisher:
Step into a world of horror with Dead of Night, a small box expansion for Arkham Horror!
In Dead of Night, investigators explore the facets of Arkham best left unseen in the light of day. Organized crime builds a strong foothold in the city, secret cults labor for a dark master, an alien moon hangs overhead, and unknowable horrors stalk the night. This expansion includes two all-new scenarios, new encounters for every location in Arkham, new monsters and anomalies, and four new investigators to face these fresh horrors, armed with new spells, items, and allies.