First Family by David Baldacci is the 4th installment in the series featuring Sean King and Michelle Maxwell.
This book had a publication date of April 21, 2009 and was yet another NYT bestseller by Baldacci.
First Family book description
A daring kidnapping turns a children’s birthday party at Camp David, the presidential retreat, into a national security nightmare.
Former Secret Service agents turned private investigators, Sean King and Michelle Maxwell don’t want to get involved. But years ago Sean King saved the First Lady’s husband, then a senator, from political disaster.
Now the president’s wife presses Sean and Michelle into a desperate search to rescue a kidnapped child.
With Michelle still battling her own demons, the two are pushed to the limit, with forces aligned on all sides against them – and the line between friend and foe impossible to define… or defend.