Duplicity by Lisa Phillips

A score to settle.
Vanguard technical specialist Simon Olson has spent years working to make up for the mistakes he made. With his twin about to marry the love of his life, Simon has one last job to do, and he’ll be able to let go enough to move on without the past hanging over his head. Too bad it means going to high school for the first time…as a teacher.
A battle for truth.
Officer Catalina Alvarez is the East Benson High school resource officer. Even with the legacy of police service in her blood, it still seems as if everyone expects her to prove herself. Cat has found her place walking the mean streets…uh, halls…of high school. Still, the death of her partner and conviction of the kid who confessed to shooting them both never quite fit. If she finds the real killer, she’ll finally be able to let the past rest in peace.
As Simon hunts for the server hosting the criminal technology he invented, his new boss at Vanguard discovers what he’s doing and gives him an ultimatum. Cat is called to the scene of a missing teen girl, one of several abducted recently, allowing Vanguard and the police to join forces to fight a new threat—putting Cat and Simon in the middle when it all breaks open.
Simon finally gets his shot at taking down the communication network. But will the price of victory be too high?