Scream For Me by Karen Rose

What the cover says:
Special Agent Daniel Vartanian has made a horrific discovery - photographs, taken years ago by his brother Simon, showing a gang of teenagers raping young girls. Disgusted, Vartanian is determined to bring the rapists to justice.
Alex Fallon's family fell apart when her sister was murdered thirteen years ago. And history now seems to be repeating itself with her stepsister Bailey's disappearance. When Vartanian meets Alex, and realises that her dead sister was in the photos, he starts to believe that the rapists may be behind Bailey's disappearance.
Bailey Crighton is being held captive by a monster. Alone and unable to escape, all she can do is scream for help. Vartanian and Alex must confront their pasts head-on if they are to find Bailey - before it's too late...

Excitement from beginning to end. It does get rather confusing at times, particularly with the use of code names, but this really is part of the story, and it wouldn't work as well otherwise. Gripping and unputdownable.

9/10