Oath of Loyalty (Mitch Rapp 21) by Vince Flynn

Named the Best Thriller of 2022 by The Real Book Spy
Mitch Rapp—“the best hero the thriller genre has to offer” (The Real Book Spy)—confronts a very different kind of killer in this explosive addition to Vince Flynn’s #1 New York Times bestselling series, written by Kyle Mills.
With President Anthony Cook convinced that Mitch Rapp poses a mortal threat to him, CIA Director Irene Kennedy is forced to construct a truce between the two men. The terms are simple: Rapp agrees to leave the country and stay in plain sight for as long as Cook controls the White House. In exchange, the administration agrees not to make any moves against him.
This fragile détente holds until Cook’s power-hungry security adviser convinces him that Rapp has no intention of honoring their agreement. To put him on the defensive, they leak the identity of his partner, Claudia Gould. As Rapp races to neutralize the enemies organizing against her, he discovers that a new type of assassin is on her trail.
Known only as Legion, the shadowy killer has created a business model based on double-blind secrecy. Neither the assassin nor the client knows the other’s identity. Because of this, Legion can’t be called off nor can they afford to fail. No matter how long it takes—weeks, months, years—they won’t stand down until their target is dead. Faced with the seemingly impossible task of finding and stopping Legion, Rapp and his people must close ranks against a world that has turned on them.