Mission critical

Court Gentry's flight on a CIA transport plane is interrupted when a security team brings a hooded man aboard.  They want to kick Gentry off the flight but are overruled by CIA headquarters.  The mystery man is being transported to England where a joint CIA/MI6 team will interrogate him about a mole in Langley. 

When they land in an isolated airbase in the U.K., they are attacked by a hostile force who kidnaps the prisoner.  Only Gentry escapes.  His handlers send him after the attackers, but what can one operative do against a trained team of assassins?  A lot, when that operative is the Gray Man.