Cross Down — James Patterson

Alex Cross is gravely injured. Only his partner and friend John Sampson can keep him safe . . . and get him justice.

For the first time, John Sampson is on his own. 
 
The brilliant crime-solving duo of Washington, DC's, Metro PD and the FBI has a proven MO: Detective Alex Cross makes his own rules. Detective John Sampson enforces them.
 
When military-style attacks erupt, brutally sidelining Cross, Sampson is sent reeling. The patterns are too random -- Sampson's friend, his partner, his brother -- have told him. Don't trust anyone. 
 
As a shadow force advances on the nation's capital, Sampson alone must protect the Cross family, his own young daughter, and every American, including the president.