Showing Before Cain Strikes by Joshua Corin

When the student is ready, the teacher appears. The only problem is, in this online classroom the students are would-be serial killers eager to learn the tricks of the trade from a master, the enigmatic Cain42.

FBI consultant Esme Stuart is struggling to stanch the doubt and fear eating away at her marriage. Now a seedy true-crime writer is dredging up the deadly confrontation that nearly destroyed her. But the link between Esme's old enemy and this new predator is the key to the Bureau's manhunt.

Esme knows her involvement in the case could cost her everything. Her marriage. Her daughter. Her life. But when Cain openly challenges his "students" to embark on a killing spree, she has no choice but to act–before Cain strikes another victim down…