From the back of the box:
Detailing hand-to-hand melee weapons, firearms, and Cthulhu Mythos artifacts. Each card describes the weapon's game statistics, as well as supporting historical information (48 cards).
Call of Cthulhu Keeper Decks are designed to provide in game [sic] resources, handy references, and information. Use these decks to supplement scenarios, for inspiration when designing new encounters, to pass secret and important notes to players, and as a handy way to impart information. These decks can add new layers to plots, enhance the story, as well as [sic] introduce friendly or villainous non-player characters. Other decks in the series include: The Curious Characters Deck, The Phobia Deck, and The Unfortunate Events Deck.