Sherlock Holmes: The Breath of God (Further Advent/Sherlock Holmes) by Guy Adams.
Description: When several leading society figures begin acting out of character, Holmes is enlisted on an investigation that will see him team up with famed ghost hunter Thomas Carnacki, and the famous occultist Aleister Crowley.
As London fills up with mindless zombies, possessed by the spirits in the air, Holmes must descend beneath the city via the new underground train network to combat the source.
Read an excerpt at Fangoria.
Order from Amazon USA