Book 1 of the Call of Cthulhu Nocturnum series.
From the back of the book:
"The NOCTURNUM campaign introduces a new alien evil to your Call of Cthulhu game. LONG SHADES, the first book in this campaign, contains a wealth of background material on this malignant new force, as well as three complete adventures: Snowflake Valley, The Madness of The Twilight Queen and Stillness. Each highly-detailed adventure can be played as part of a longer campaign, or as a stand-alone adventure in your current campaign.
"LONG SHADES is a postmodern campaign sourcebook for the Call of Cthulhu roleplaying game. The background and adventures detailed in LONG SHADES are also easily adaptable to most other horror roleplaying systems."
Adventure 1: Snowflake Valley
Adventure 2: The Madness of the Twighlight Queen
Adventure 3: Stillness