Laying Down the Law by Ann Voss Peterson
Chicago Confidential #2
 
There Was Only One Law in Town
One night of explosive passion - that was all top-secret Chicago Confidential agent Lawson Davies ever had with beautiful research scientist Caroline Van Buren. That was five years ago, when they were on opposite sides of a courtroom battle. Now Law had been given an impossible mission: to pose as Caroline's husband to extricate her from an evil cult that had kidnapped and brainwashed her. With one earth-shattering kiss, however, the pretense became all too real. But with Caroline's life on the line and a killer on their heels, would "till death do us part" come true too soon?
 
4.18