Relentless (Gray Man Book 10) by Mark Greaney

Intelligence operatives around the world are disappearing. When a missing American agent re-appears in Venezuela, Court Gentry, the Gray Man, is dispatched to bring him in, but a team of assassins has other ideas. Court escapes with his life and a vital piece of intelligence.

Meanwhile, CIA agent Zoya Zakharova is in Berlin. Her mission: to infiltrate a private intelligence firm with some alarming connections. The closer she gets to answers, the less likely she is to get out alive.

Court and Zoya are just two pieces on this international chessboard, and they're about to discover one undeniable truth—sometimes capturing a king requires sacrificing some pawns.