The Spirit in St. Louis — Mark Everett Stone

The whole world now knows of the existence of the World Under, thanks to fallout from the terrible events in Omaha a year back. As the World Under's most effective foe, Kal Hakala performed actions that were both heroic and horrific. Now, sidelined as an Agent, he serves the Bureau of Supernatural Investigation as its public face, charming talk show hosts and training new recruits known as “Green Peas.” However, the World Under never rests, and events force Kal back into action. A malevolent spirit occupies St. Louis's Quint Building, and the team sent in to combat it disappears after their leader is driven to suicide. The BSI has no choice but to send in Kalevi Hakala and his team to solve the problem. As each of the individual members of Kal's team is isolated and dumped into his or her private hell, Kal begins to wonder if he hasn't finally met his match: the most powerful force the World Under has to offer. Book 6 in the From the Files of the BSI series.