The Todd Chronicles — Elena Santangelo

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 Dr. Ziegler needs a faithful sidekick to chronicle her cases, even if she's determined to work alone. Together they solve robberies, assaults, murders and other mysterious goings-on while Todd tries to crack the ultimate enigma, Dr. Ziegler herself. This is the 2nd book in the Twins Mystery Series.