Deadly Challenge by Trish Kocialski

In Deadly Challenge, Dean and Katie return to Virginia after their week of rest and relaxation in the Bahamas. Katie is starting a new job with the DEA as an instructor at the training center in Quantico, while Dean returns to the Pentagon and her Intelligence work. Trying to organize things in their new routine, their lives are soon turned upside down, when vicious acts of violence target their close friends and attempt to tear apart their personal relationship. As the women try to decipher all of the pieces of the puzzle, their search is complicated by the demands of their careers and an unexpected request from Dean’s estranged father.

Dean is forced to accept a deadly challenge and race against time to find her lover, as the action escalates to a thundering climax at Niagara Falls.