The First Lady by Jas Patterson & B. Dubois

I was just in the mood for some summer fluff reading and found The First Lady. It starts with the President of the United States being caught having an affair right before he's up for reelection. The First Lady is furious about being humiliated publicly--then she disappears. Was it intentional? Was it foul play? Sally Grissom of the Secret Service is coerced into investigating under the radar by the President and his slimy chief of staff. Sally soon realizes that the chief of staff may have his own nefarious plans in mind for the First Lady--so she's determined to find her first and keep her safe. I figured out some of the "surprise" twists before they were revealed, but it was an interesting story that would be a good beach book.