The Todd Chronicles (Twins Mystery Series #2)

Todd MacBride, a geeky undergrad psych major at the University of Arizona, imagines himself as Dr. Watson. His Holmes is Gen Ziegler, a prof and criminal psychologist who assists the Tucson police. Todd decides that Gen needs a faithful sidekick to chronicle her cases. This book is a sort of prequel to TWO-FACED, but it's strongly recommended that TWO-FACED be read FIRST.