Simple Genius by David Baldacci
The new Baldacci reintroduces the main characters from Split Second and Hour Game - the novel that took Baldacci to another level in paperback in the UK.
Sean King and Michelle Maxwell both bear the scars of their previous case. Michelle is in a psychiatric hospital after making a suicide attempt while Sean, down on his luck and desperately worried about his friend, accepts a PI job at Babbage Town - a hugely secret establishment where, it seems, corpses turn up more quickly than new codes can be encrypted by the genius mathematicians who are employed in the place . . .
While Michelle's psychiatrist determines the key to her deep depression lies in events suppressed during her childhood, Michelle uncovers something truly disturbing happening in the hospital pharmacy . . .
And with both the FBI and CIA making their presence felt in Babbage Town, Sean begins to wonder what really goes on there. But there is a place even more sinister close by, Camp Peary, where it is said CIA death squads train . . .