Book excerpt: Tom Clancy's Op-Center: Call to Treason is yet another gripping addition to the bestselling series masterminded by Tom Clancy and Steve Pieczenik. The Op-Center's budget is slashed, leaving General Mike Rodgers in the market for a new job. When presidential candidiate Senator Donald Orr recruits Rodgers to act as his military advisor, it sounds like a perfect transition. There's just one problem. A spree of deaths may be tied to Orr's presidential run and Rodgers must decide whether to sign on or shut it down.