The Cards from the Smoke are a deck of cards beautifully illustrated with the imagery from Cthulhu Britannica, which you can use to several different ends in your Call of Cthulhu games, from handling chases in a visual, exciting way, to an alternative way to run an investigation.
The simplest way to use The Cards from the Smoke is as a source of inspiration for writing a scenario - especially when you need to come up with one on the fly. Each of the cards is beautifully illustrated, complete with an evocative quote, so just rifling through the deck is bound to get the ideas flowing. Or you can shuffle the deck together and draw a handful of cards and think up a scenario based on what you draw, letting the card text and art inspire you. And, for good measure, many of the cards point you at pages in the Cthulhu Britannica: London boxed set where you'll find even more ideas.