Escape

Description for ESCAPE by James Patterson with David Ellis:

As Chicago PD's special-ops leader, Detective Billy Harney knows well that money is not the only valuable currency. The filthy rich man he's investigating is down to his last twenty million. He's also being held in jail.

For now.

Billy's unit is called in when an escape plan results in officers down and inmates vanished.

In an empty lot, Billy spots two Kevlar vests. Two helmets. Two assault rifles. And a handwritten note:

Hi, Billy
Are you having fun yet?

This is #3 in A Black Book Thriller.